chrome: Standardize fullscreen transition behavor/callbacks (fixes #3571)

Use the same code path for all fullscreen transitions so that Chrome UI updates
correctly. All user-initiated fullscreen transitions now result in
CefWindowDelegate::OnWindowFullscreenTransition callbacks.

libcef/browser/chrome/browser_delegate.h

@@ -126,6 +126,9 @@ class BrowserDelegate : public content::WebContentsDelegate {
   // Set the draggable region relative to web contents.
   // Called from DraggableRegionsHostImpl::UpdateDraggableRegions.
   virtual void UpdateDraggableRegion(const SkRegion& region) {}
+
+  // Called at the end of a fullscreen transition.
+  virtual void WindowFullscreenStateChanged() {}
 };
 
 }  // namespace cef

libcef/browser/chrome/chrome_browser_delegate.cc

@@ -15,6 +15,7 @@
 #include "libcef/browser/media_access_query.h"
 #include "libcef/browser/request_context_impl.h"
 #include "libcef/browser/views/browser_view_impl.h"
+#include "libcef/browser/views/window_impl.h"
 #include "libcef/common/app_manager.h"
 #include "libcef/common/frame_util.h"
 
@@ -257,6 +258,23 @@ void ChromeBrowserDelegate::UpdateDraggableRegion(const SkRegion& region) {
   draggable_region_ = region;
 }
 
+void ChromeBrowserDelegate::WindowFullscreenStateChanged() {
+  // Use a synchronous callback for notification on Windows/Linux. MacOS gets
+  // notified asynchronously via CefNativeWidgetMac callbacks.
+#if !BUILDFLAG(IS_MAC)
+  if (auto browser = ChromeBrowserHostImpl::GetBrowserForBrowser(browser_)) {
+    if (auto chrome_browser_view = browser->chrome_browser_view()) {
+      auto* cef_window = chrome_browser_view->cef_browser_view()->cef_window();
+      if (auto* delegate = cef_window->delegate()) {
+        // Give the CefWindowDelegate a chance to handle the event.
+        delegate->OnWindowFullscreenTransition(cef_window,
+                                               /*is_completed=*/true);
+      }
+    }
+  }
+#endif
+}
+
 void ChromeBrowserDelegate::WebContentsCreated(
     content::WebContents* source_contents,
     int opener_render_process_id,

libcef/browser/chrome/chrome_browser_delegate.h

@@ -70,6 +70,7 @@ class ChromeBrowserDelegate : public cef::BrowserDelegate {
   bool SupportsDraggableRegion() const override;
   const absl::optional<SkRegion> GetDraggableRegion() const override;
   void UpdateDraggableRegion(const SkRegion& region) override;
+  void WindowFullscreenStateChanged() override;
 
   // WebContentsDelegate methods:
   void WebContentsCreated(content::WebContents* source_contents,

libcef/browser/chrome/views/chrome_browser_frame.cc

@@ -6,6 +6,7 @@
 
 #include "chrome/browser/themes/theme_service.h"
 #include "chrome/browser/ui/browser.h"
+#include "chrome/browser/ui/browser_commands.h"
 #include "chrome/browser/ui/views/frame/browser_view.h"
 
 #if BUILDFLAG(IS_MAC)
@@ -17,10 +18,10 @@
 void ChromeBrowserFrame::Init(BrowserView* browser_view,
                               std::unique_ptr<Browser> browser) {
   DCHECK(browser_view);
+  DCHECK(browser);
 
-  DCHECK(!browser_);
-  browser_ = browser.get();
-  DCHECK(browser_);
+  DCHECK(!browser_view_);
+  browser_view_ = browser_view;
 
   // Initialize BrowserFrame state.
   InitBrowserView(browser_view);
@@ -42,6 +43,10 @@ void ChromeBrowserFrame::Init(BrowserView* browser_view,
 #endif  // BUILDFLAG(IS_MAC)
 }
 
+void ChromeBrowserFrame::ToggleFullscreenMode() {
+  chrome::ToggleFullscreenMode(browser_view_->browser());
+}
+
 views::internal::RootView* ChromeBrowserFrame::CreateRootView() {
   // Bypass the BrowserFrame implementation.
   return views::Widget::CreateRootView();

libcef/browser/chrome/views/chrome_browser_frame.h

@@ -97,13 +97,17 @@ class ChromeBrowserFrame : public BrowserFrame {
 
   void Init(BrowserView* browser_view, std::unique_ptr<Browser> browser);
 
+  void ToggleFullscreenMode();
+
   // views::Widget methods:
   views::internal::RootView* CreateRootView() override;
   std::unique_ptr<views::NonClientFrameView> CreateNonClientFrameView()
       override;
 
+  BrowserView* browser_view() const { return browser_view_; }
+
  private:
-  Browser* browser_ = nullptr;
+  BrowserView* browser_view_ = nullptr;
 };
 
 #endif  // CEF_LIBCEF_BROWSER_CHROME_VIEWS_CHROME_BROWSER_FRAME_H_