diff --git content/browser/renderer_host/render_widget_host_view_base.cc content/browser/renderer_host/render_widget_host_view_base.cc
index 999eeb6fc817a..8a0c56bc23bcb 100644
--- content/browser/renderer_host/render_widget_host_view_base.cc
+++ content/browser/renderer_host/render_widget_host_view_base.cc
@@ -662,6 +662,14 @@ float RenderWidgetHostViewBase::GetScaleOverrideForCapture() const {
   return scale_override_for_capture_;
 }
 
+void RenderWidgetHostViewBase::SetHasExternalParent(bool val) {
+  has_external_parent_ = val;
+}
+
+bool RenderWidgetHostViewBase::HasExternalParent() const {
+  return has_external_parent_;
+}
+
 void RenderWidgetHostViewBase::OnAutoscrollStart() {
   if (!GetMouseWheelPhaseHandler())
     return;
diff --git content/browser/renderer_host/render_widget_host_view_base.h content/browser/renderer_host/render_widget_host_view_base.h
index f3a4f3961b543..4ac493f0f03da 100644
--- content/browser/renderer_host/render_widget_host_view_base.h
+++ content/browser/renderer_host/render_widget_host_view_base.h
@@ -68,6 +68,7 @@ class CursorManager;
 class MouseWheelPhaseHandler;
 class RenderWidgetHostImpl;
 class RenderWidgetHostViewBaseObserver;
+class RenderWidgetHostViewGuest;
 class SyntheticGestureTarget;
 class TextInputManager;
 class TouchSelectionControllerClientManager;
@@ -140,6 +141,8 @@ class CONTENT_EXPORT RenderWidgetHostViewBase : public RenderWidgetHostView {
                         const gfx::Size& max_size) override;
   void DisableAutoResize(const gfx::Size& new_size) override;
   float GetDeviceScaleFactor() const final;
+  void SetHasExternalParent(bool val) override;
+  bool HasExternalParent() const override;
   TouchSelectionControllerClientManager*
   GetTouchSelectionControllerClientManager() override;
   bool ShouldVirtualKeyboardOverlayContent() override;
@@ -176,6 +179,10 @@ class CONTENT_EXPORT RenderWidgetHostViewBase : public RenderWidgetHostView {
   // Called when screen information or native widget bounds change.
   virtual void UpdateScreenInfo();
 
+  // Generates the most current set of ScreenInfos from the current set of
+  // displays in the system for use in UpdateScreenInfo.
+  virtual display::ScreenInfos GetNewScreenInfosForUpdate();
+
   // Called by the TextInputManager to notify the view about being removed from
   // the list of registered views, i.e., TextInputManager is no longer tracking
   // TextInputState from this view. The RWHV should reset |text_input_manager_|
@@ -432,6 +439,12 @@ class CONTENT_EXPORT RenderWidgetHostViewBase : public RenderWidgetHostView {
                            const gfx::Rect& bounds,
                            const gfx::Rect& anchor_rect) = 0;
 
+  // Perform all the initialization steps necessary for this object to represent
+  // the platform widget owned by |guest_view| and embedded in
+  // |parent_host_view|.
+  virtual void InitAsGuest(RenderWidgetHostView* parent_host_view,
+                           RenderWidgetHostViewGuest* guest_view) {}
+
   // Sets the cursor for this view to the one associated with the specified
   // cursor_type.
   virtual void UpdateCursor(const WebCursor& cursor) = 0;
@@ -674,6 +687,10 @@ class CONTENT_EXPORT RenderWidgetHostViewBase : public RenderWidgetHostView {
   // to all displays.
   gfx::Size system_cursor_size_;
 
+  // True if the widget has a external parent view/window outside of the
+  // Chromium-controlled view/window hierarchy.
+  bool has_external_parent_ = false;
+
  private:
   FRIEND_TEST_ALL_PREFIXES(
       BrowserSideFlingBrowserTest,
@@ -695,10 +712,6 @@ class CONTENT_EXPORT RenderWidgetHostViewBase : public RenderWidgetHostView {
 
   void SynchronizeVisualProperties();
 
-  // Generates the most current set of ScreenInfos from the current set of
-  // displays in the system for use in UpdateScreenInfo.
-  display::ScreenInfos GetNewScreenInfosForUpdate();
-
   // Called when display properties that need to be synchronized with the
   // renderer process changes. This method is called before notifying
   // RenderWidgetHostImpl in order to allow the view to allocate a new
diff --git content/browser/renderer_host/render_widget_host_view_event_handler.cc content/browser/renderer_host/render_widget_host_view_event_handler.cc
index 80f8f5d2be88d..7b3ec5e68ab4b 100644
--- content/browser/renderer_host/render_widget_host_view_event_handler.cc
+++ content/browser/renderer_host/render_widget_host_view_event_handler.cc
@@ -52,6 +52,10 @@ namespace {
 // of the border area, in percentage of the corresponding dimension.
 const int kMouseLockBorderPercentage = 15;
 
+#if BUILDFLAG(IS_LINUX)
+#include "ui/aura/window_tree_host.h"
+#endif
+
 #if BUILDFLAG(IS_WIN)
 // A callback function for EnumThreadWindows to enumerate and dismiss
 // any owned popup windows.
@@ -833,6 +837,14 @@ void RenderWidgetHostViewEventHandler::MoveCursorToCenter(
     }
     return;
   }
+#endif
+#if BUILDFLAG(IS_LINUX)
+  if (host_view_->HasExternalParent() &&
+      window_ && window_->delegate()->CanFocus()) {
+    aura::WindowTreeHost* host = window_->GetHost();
+    if (host)
+      host->Show();
+  }
 #endif
   synthetic_move_position_ = center_in_screen;
 }
@@ -862,6 +874,17 @@ bool RenderWidgetHostViewEventHandler::MatchesSynthesizedMovePosition(
 }
 
 void RenderWidgetHostViewEventHandler::SetKeyboardFocus() {
+#if BUILDFLAG(IS_WIN)
+  if (host_view_->HasExternalParent() &&
+      window_ && window_->delegate()->CanFocus()) {
+    aura::WindowTreeHost* host = window_->GetHost();
+    if (host) {
+      gfx::AcceleratedWidget hwnd = host->GetAcceleratedWidget();
+      if (!(::GetWindowLong(hwnd, GWL_EXSTYLE) & WS_EX_NOACTIVATE))
+        ::SetFocus(hwnd);
+    }
+  }
+#endif
   // TODO(wjmaclean): can host_ ever be null?
   if (host_ && set_focus_on_mouse_down_or_key_event_) {
     set_focus_on_mouse_down_or_key_event_ = false;
diff --git content/public/browser/render_widget_host_view.h content/public/browser/render_widget_host_view.h
index 5d291f223feba..1999fbc5bf67a 100644
--- content/public/browser/render_widget_host_view.h
+++ content/public/browser/render_widget_host_view.h
@@ -257,6 +257,14 @@ class CONTENT_EXPORT RenderWidgetHostView {
   // This must always return the same device scale factor as GetScreenInfo.
   virtual float GetDeviceScaleFactor() const = 0;
 
+  // Set whether the widget has a external parent view/window outside of the
+  // Chromium-controlled view/window hierarchy.
+  virtual void SetHasExternalParent(bool val) = 0;
+
+  // Returns true if the widget has a external parent view/window outside of the
+  // Chromium-controlled view/window hierarchy.
+  virtual bool HasExternalParent() const = 0;
+
 #if BUILDFLAG(IS_MAC)
   // Set the view's active state (i.e., tint state of controls).
   virtual void SetActive(bool active) = 0;
diff --git ui/ozone/platform/x11/x11_window.cc ui/ozone/platform/x11/x11_window.cc
index 6c1689e6ab2e2..7933acdd2eac9 100644
--- ui/ozone/platform/x11/x11_window.cc
+++ ui/ozone/platform/x11/x11_window.cc
@@ -1774,7 +1774,8 @@ void X11Window::CreateXWindow(const PlatformWindowInitProperties& properties) {
   req.border_pixel = 0;
 
   bounds_in_pixels_ = SanitizeBounds(bounds);
-  req.parent = x_root_window_;
+  req.parent = properties.parent_widget == gfx::kNullAcceleratedWidget ?
+      x_root_window_ : static_cast<x11::Window>(properties.parent_widget);
   req.x = bounds_in_pixels_.x();
   req.y = bounds_in_pixels_.y();
   req.width = bounds_in_pixels_.width();
diff --git ui/views/widget/desktop_aura/desktop_screen_win.cc ui/views/widget/desktop_aura/desktop_screen_win.cc
index 87a4458f9fbfc..bc3edd88fac7f 100644
--- ui/views/widget/desktop_aura/desktop_screen_win.cc
+++ ui/views/widget/desktop_aura/desktop_screen_win.cc
@@ -23,6 +23,8 @@ DesktopScreenWin::~DesktopScreenWin() {
 }
 
 HWND DesktopScreenWin::GetHWNDFromNativeWindow(gfx::NativeWindow window) const {
+  if (!window)
+    return nullptr;
   aura::WindowTreeHost* host = window->GetHost();
   return host ? host->GetAcceleratedWidget() : nullptr;
 }
diff --git ui/views/widget/desktop_aura/desktop_window_tree_host_linux.cc ui/views/widget/desktop_aura/desktop_window_tree_host_linux.cc
index 5cb499fa35436..38659ad852b10 100644
--- ui/views/widget/desktop_aura/desktop_window_tree_host_linux.cc
+++ ui/views/widget/desktop_aura/desktop_window_tree_host_linux.cc
@@ -164,6 +164,18 @@ Widget::MoveLoopResult DesktopWindowTreeHostLinux::RunMoveLoop(
   return result;
 }
 
+gfx::Rect DesktopWindowTreeHostLinux::GetWindowBoundsInScreen() const {
+  if (!screen_bounds_.IsEmpty())
+    return screen_bounds_;
+  return DesktopWindowTreeHostPlatform::GetWindowBoundsInScreen();
+}
+
+gfx::Point DesktopWindowTreeHostLinux::GetLocationOnScreenInPixels() const {
+  if (!screen_bounds_.IsEmpty())
+    return screen_bounds_.origin();
+  return DesktopWindowTreeHostPlatform::GetLocationOnScreenInPixels();
+}
+
 void DesktopWindowTreeHostLinux::DispatchEvent(ui::Event* event) {
   // In Windows, the native events sent to chrome are separated into client
   // and non-client versions of events, which we record on our LocatedEvent
@@ -289,6 +301,8 @@ void DesktopWindowTreeHostLinux::AddAdditionalInitProperties(
 
   properties->wayland_app_id = params.wayland_app_id;
 
+  properties->parent_widget = params.parent_widget;
+
   DCHECK(!properties->x11_extension_delegate);
   properties->x11_extension_delegate = this;
 }
diff --git ui/views/widget/desktop_aura/desktop_window_tree_host_linux.h ui/views/widget/desktop_aura/desktop_window_tree_host_linux.h
index e6842b0848c74..d214247587d41 100644
--- ui/views/widget/desktop_aura/desktop_window_tree_host_linux.h
+++ ui/views/widget/desktop_aura/desktop_window_tree_host_linux.h
@@ -57,6 +57,8 @@ class VIEWS_EXPORT DesktopWindowTreeHostLinux
   // Disables event listening to make |dialog| modal.
   base::OnceClosure DisableEventListening();
 
+  void set_screen_bounds(const gfx::Rect& bounds) { screen_bounds_ = bounds; }
+
  protected:
   // Overridden from DesktopWindowTreeHost:
   void Init(const Widget::InitParams& params) override;
@@ -66,6 +68,8 @@ class VIEWS_EXPORT DesktopWindowTreeHostLinux
       const gfx::Vector2d& drag_offset,
       Widget::MoveLoopSource source,
       Widget::MoveLoopEscapeBehavior escape_behavior) override;
+  gfx::Rect GetWindowBoundsInScreen() const override;
+  gfx::Point GetLocationOnScreenInPixels() const override;
 
   // PlatformWindowDelegate:
   void DispatchEvent(ui::Event* event) override;
@@ -112,6 +116,9 @@ class VIEWS_EXPORT DesktopWindowTreeHostLinux
 
   uint32_t modal_dialog_counter_ = 0;
 
+   // Override the screen bounds when the host is a child window.
+  gfx::Rect screen_bounds_;
+
   // The display and the native X window hosting the root window.
   base::WeakPtrFactory<DesktopWindowTreeHostLinux> weak_factory_{this};
 };
diff --git ui/views/widget/desktop_aura/desktop_window_tree_host_platform.cc ui/views/widget/desktop_aura/desktop_window_tree_host_platform.cc
index cfdf2f5682ee3..c36ea9dd07ac9 100644
--- ui/views/widget/desktop_aura/desktop_window_tree_host_platform.cc
+++ ui/views/widget/desktop_aura/desktop_window_tree_host_platform.cc
@@ -272,8 +272,8 @@ void DesktopWindowTreeHostPlatform::Init(const Widget::InitParams& params) {
   if (properties.parent_widget) {
     window_parent_ = DesktopWindowTreeHostPlatform::GetHostForWidget(
         properties.parent_widget);
-    DCHECK(window_parent_);
-    window_parent_->window_children_.insert(this);
+    if (window_parent_)
+      window_parent_->window_children_.insert(this);
   }
 
   // Calculate initial bounds.
diff --git ui/views/widget/desktop_aura/desktop_window_tree_host_win.cc ui/views/widget/desktop_aura/desktop_window_tree_host_win.cc
index b6d243983474c..0a5092598e69f 100644
--- ui/views/widget/desktop_aura/desktop_window_tree_host_win.cc
+++ ui/views/widget/desktop_aura/desktop_window_tree_host_win.cc
@@ -181,8 +181,12 @@ void DesktopWindowTreeHostWin::Init(const Widget::InitParams& params) {
                         native_widget_delegate_);
 
   HWND parent_hwnd = nullptr;
-  if (params.parent && params.parent->GetHost())
+  if (params.parent_widget) {
+    parent_hwnd = params.parent_widget;
+    has_external_parent_ = true;
+  } else if (params.parent && params.parent->GetHost()) {
     parent_hwnd = params.parent->GetHost()->GetAcceleratedWidget();
+  }
 
   remove_standard_frame_ = params.remove_standard_frame;
   has_non_client_view_ = Widget::RequiresNonClientView(params.type);
@@ -989,11 +993,15 @@ void DesktopWindowTreeHostWin::HandleFrameChanged() {
 }
 
 void DesktopWindowTreeHostWin::HandleNativeFocus(HWND last_focused_window) {
-  // TODO(beng): inform the native_widget_delegate_.
+  // See comments in CefBrowserPlatformDelegateNativeWin::SetFocus.
+  if (has_external_parent_ && CanActivate())
+    HandleActivationChanged(true);
 }
 
 void DesktopWindowTreeHostWin::HandleNativeBlur(HWND focused_window) {
-  // TODO(beng): inform the native_widget_delegate_.
+  // See comments in CefBrowserPlatformDelegateNativeWin::SetFocus.
+  if (has_external_parent_ && CanActivate())
+    HandleActivationChanged(false);
 }
 
 bool DesktopWindowTreeHostWin::HandleMouseEvent(ui::MouseEvent* event) {
@@ -1001,6 +1009,12 @@ bool DesktopWindowTreeHostWin::HandleMouseEvent(ui::MouseEvent* event) {
   if (ui::PlatformEventSource::ShouldIgnoreNativePlatformEvents())
     return true;
 
+  // See comments in CefBrowserPlatformDelegateNativeWin::SetFocus.
+  if (has_external_parent_ && CanActivate() && event->IsAnyButton() &&
+      ::GetFocus() != GetHWND()) {
+    ::SetFocus(GetHWND());
+  }
+
   SendEventToSink(event);
   return event->handled();
 }
diff --git ui/views/widget/desktop_aura/desktop_window_tree_host_win.h ui/views/widget/desktop_aura/desktop_window_tree_host_win.h
index 0aae49ec83b88..ab61925742ed7 100644
--- ui/views/widget/desktop_aura/desktop_window_tree_host_win.h
+++ ui/views/widget/desktop_aura/desktop_window_tree_host_win.h
@@ -324,6 +324,10 @@ class VIEWS_EXPORT DesktopWindowTreeHostWin
   // True if the window should have the frame removed.
   bool remove_standard_frame_;
 
+  // True if the widget has a external parent view/window outside of the
+  // Chromium-controlled view/window hierarchy.
+  bool has_external_parent_ = false;
+
   // Owned by TooltipController, but we need to forward events to it so we keep
   // a reference.
   raw_ptr<corewm::TooltipWin> tooltip_;
diff --git ui/views/widget/widget.cc ui/views/widget/widget.cc
index 2cb71ae39fa7b..dcb03c59fde50 100644
--- ui/views/widget/widget.cc
+++ ui/views/widget/widget.cc
@@ -338,7 +338,8 @@ void Widget::Init(InitParams params) {
   }
 
   params.child |= (params.type == InitParams::TYPE_CONTROL);
-  is_top_level_ = !params.child;
+  is_top_level_ = !params.child ||
+                  params.parent_widget != gfx::kNullAcceleratedWidget;
 
   if (params.opacity == views::Widget::InitParams::WindowOpacity::kInferred &&
       params.type != views::Widget::InitParams::TYPE_WINDOW) {
@@ -417,13 +418,21 @@ void Widget::Init(InitParams params) {
 
     if (show_state == ui::SHOW_STATE_MAXIMIZED) {
       Maximize();
+      saved_show_state_ = ui::SHOW_STATE_MAXIMIZED;
     } else if (show_state == ui::SHOW_STATE_MINIMIZED) {
       Minimize();
       saved_show_state_ = ui::SHOW_STATE_MINIMIZED;
+    } else if (show_state == ui::SHOW_STATE_FULLSCREEN) {
+      SetFullscreen(true);
     }
   } else if (delegate) {
     SetContentsView(delegate->TransferOwnershipOfContentsView());
-    SetInitialBoundsForFramelessWindow(bounds);
+    if (params.parent_widget != gfx::kNullAcceleratedWidget) {
+      // Set the bounds directly instead of applying an inset.
+      SetBounds(bounds);
+    } else {
+      SetInitialBoundsForFramelessWindow(bounds);
+    }
   }
 
   native_theme_observation_.Observe(GetNativeTheme());
@@ -1434,10 +1443,16 @@ void Widget::OnNativeWidgetParentChanged(gfx::NativeView parent) {
 }
 
 gfx::Size Widget::GetMinimumSize() const {
+  gfx::Size size;
+  if (widget_delegate_->MaybeGetMinimumSize(&size))
+    return size;
   return non_client_view_ ? non_client_view_->GetMinimumSize() : gfx::Size();
 }
 
 gfx::Size Widget::GetMaximumSize() const {
+  gfx::Size size;
+  if (widget_delegate_->MaybeGetMaximumSize(&size))
+    return size;
   return non_client_view_ ? non_client_view_->GetMaximumSize() : gfx::Size();
 }
 
diff --git ui/views/widget/widget.h ui/views/widget/widget.h
index 6e8a17f9452fb..0e45f3c72b3c2 100644
--- ui/views/widget/widget.h
+++ ui/views/widget/widget.h
@@ -337,6 +337,8 @@ class VIEWS_EXPORT Widget : public internal::NativeWidgetDelegate,
     // the concept with bubble anchoring a la BubbleDialogDelegateView.
     gfx::NativeView parent = nullptr;
 
+    gfx::AcceleratedWidget parent_widget = gfx::kNullAcceleratedWidget;
+
     // Specifies the initial bounds of the Widget. Default is empty, which means
     // the NativeWidget may specify a default size. If the parent is specified,
     // |bounds| is in the parent's coordinate system. If the parent is not
diff --git ui/views/widget/widget_delegate.h ui/views/widget/widget_delegate.h
index 431d19f2543a9..4e2e69a650118 100644
--- ui/views/widget/widget_delegate.h
+++ ui/views/widget/widget_delegate.h
@@ -375,6 +375,10 @@ class VIEWS_EXPORT WidgetDelegate {
   // Returns true if the title text should be centered.
   bool ShouldCenterWindowTitleText() const;
 
+  // CEF supports override of min/max size values.
+  virtual bool MaybeGetMinimumSize(gfx::Size* size) const { return false; }
+  virtual bool MaybeGetMaximumSize(gfx::Size* size) const { return false; }
+
   bool focus_traverses_out() const { return params_.focus_traverses_out; }
   bool enable_arrow_key_traversal() const {
     return params_.enable_arrow_key_traversal;
diff --git ui/views/widget/widget_hwnd_utils.cc ui/views/widget/widget_hwnd_utils.cc
index 89b4b5e0ec4bc..669583f83340f 100644
--- ui/views/widget/widget_hwnd_utils.cc
+++ ui/views/widget/widget_hwnd_utils.cc
@@ -67,7 +67,8 @@ void CalculateWindowStylesFromInitParams(
       if (!widget_delegate->CanResize())
         *style &= static_cast<DWORD>(~(WS_THICKFRAME | WS_MAXIMIZEBOX));
       if (params.remove_standard_frame)
-        *style &= static_cast<DWORD>(~(WS_MINIMIZEBOX | WS_MAXIMIZEBOX));
+        *style &= static_cast<DWORD>(~(WS_MINIMIZEBOX | WS_MAXIMIZEBOX |
+                                       WS_CAPTION | WS_SYSMENU));
 
       if (native_widget_delegate->IsDialogBox()) {
         *style |= DS_MODALFRAME;
diff --git ui/views/win/hwnd_message_handler.cc ui/views/win/hwnd_message_handler.cc
index 29e812d41d5c8..4a1c3ddc1216b 100644
--- ui/views/win/hwnd_message_handler.cc
+++ ui/views/win/hwnd_message_handler.cc
@@ -825,7 +825,11 @@ bool HWNDMessageHandler::IsVisible() const {
 }
 
 bool HWNDMessageHandler::IsActive() const {
-  return GetActiveWindow() == hwnd();
+  // This active state is checked via FocusManager::SetFocusedViewWithReason.
+  // With CEF external parent hwnd() may be a child window, whereas
+  // GetActiveWindow() will return the root window, so make sure that we always
+  // compare root windows.
+  return GetActiveWindow() == GetAncestor(hwnd(), GA_ROOT);
 }
 
 bool HWNDMessageHandler::IsMinimized() const {
@@ -3221,10 +3225,13 @@ LRESULT HWNDMessageHandler::HandleMouseEventInternal(UINT message,
   } else if (event.type() == ui::ET_MOUSEWHEEL) {
     ui::MouseWheelEvent mouse_wheel_event(msg);
     // Reroute the mouse wheel to the window under the pointer if applicable.
-    return (ui::RerouteMouseWheel(hwnd(), w_param, l_param) ||
-            delegate_->HandleMouseEvent(&mouse_wheel_event))
-               ? 0
-               : 1;
+    if (ui::RerouteMouseWheel(hwnd(), w_param, l_param) ||
+        delegate_->HandleMouseEvent(&mouse_wheel_event)) {
+      SetMsgHandled(TRUE);
+      return 0;
+    } else {
+      return 1;
+    }
   }
 
   // Suppress |ET_MOUSE_MOVED| and |ET_MOUSE_DRAGGED| events from WM_MOUSE*