chrome: Add support for Alloy style browsers and windows (see #3681)

Split the Alloy runtime into bootstrap and style components. Support
creation of Alloy style browsers and windows with the Chrome runtime.
Chrome runtime (`--enable-chrome-runtime`) + Alloy style
(`--use-alloy-style`) supports Views (`--use-views`), native parent
(`--use-native`) and windowless rendering
(`--off-screen-rendering-enabled`).

Print preview is supported in all cases except with windowless rendering
on all platforms and native parent on MacOS. It is disabled by default
with Alloy style for legacy compatibility. Where supported it can be
enabled or disabled globally using `--[enable|disable]-print-preview` or
configured on a per-RequestContext basis using the
`printing.print_preview_disabled` preference. It also behaves as
expected when triggered via the PDF viewer print button.

Chrome runtime + Alloy style behavior differs from Alloy runtime in the
following significant ways:

- Supports Chrome error pages by default.
- DevTools popups are Chrome style only (cannot be windowless).
- The Alloy extension API will not supported.

Chrome runtime + Alloy style passes all expected Alloy ceftests except
the following:

- `DisplayTest.AutoResize` (Alloy extension API not supported)
- `DownloadTest.*` (Download API not yet supported)
- `ExtensionTest.*` (Alloy extension API not supported)

This change also adds Chrome runtime support for
CefContextMenuHandler::RunContextMenu (see #3293).

This change also explicitly blocks (and doesn't retry) FrameAttached
requests from PDF viewer and print preview excluded frames (see #3664).

Known issues specific to Chrome runtime + Alloy style:
- DevTools popup with windowless rendering doesn't load successfully.
  Use windowed rendering or remote debugging as a workaround.
- Chrome style Window with Alloy style BrowserView (`--use-alloy-style
  --use-chrome-style-window`) does not show Chrome theme changes.

To test:
- Run `ceftests --enable-chrome-runtime --use-alloy-style
       [--use-chrome-style-window] [--use-views|--use-native]
       --gtest_filter=...`
- Run `cefclient --enable-chrome-runtime --use-alloy-style
       [--use-chrome-style-window]
       [--use-views|--use-native|--off-screen-rendering-enabled]`
- Run `cefsimple --enable-chrome-runtime --use-alloy-style [--use-views]`

libcef/browser/browser_host_create.cc

@@ -65,8 +65,9 @@ bool CefBrowserHost::CreateBrowser(
 
   // Verify windowless rendering requirements.
   if (windowInfo.windowless_rendering_enabled &&
-      !client->GetRenderHandler().get()) {
-    DCHECK(false) << "CefRenderHandler implementation is required";
+      (!client || !client->GetRenderHandler().get())) {
+    LOG(ERROR)
+        << "Windowless rendering requires a CefRenderHandler implementation";
     return false;
   }
 
@@ -133,13 +134,15 @@ CefRefPtr<CefBrowser> CefBrowserHost::CreateBrowserSync(
 
   // Verify windowless rendering requirements.
   if (windowInfo.windowless_rendering_enabled &&
-      !client->GetRenderHandler().get()) {
-    DCHECK(false) << "CefRenderHandler implementation is required";
+      (!client || !client->GetRenderHandler().get())) {
+    LOG(ERROR)
+        << "Windowless rendering requires a CefRenderHandler implementation";
     return nullptr;
   }
 
   CefBrowserCreateParams create_params;
-  create_params.MaybeSetWindowInfo(windowInfo);
+  create_params.MaybeSetWindowInfo(windowInfo, /*allow_alloy_style=*/true,
+                                   /*allow_chrome_style=*/true);
   create_params.client = client;
   create_params.url = url;
   create_params.settings = settings;
@@ -149,18 +152,121 @@ CefRefPtr<CefBrowser> CefBrowserHost::CreateBrowserSync(
   return CefBrowserHostBase::Create(create_params);
 }
 
+// static
+bool CefBrowserCreateParams::IsChromeStyle(const CefWindowInfo* window_info) {
+  if (!cef::IsChromeRuntimeEnabled()) {
+    return false;
+  }
+  if (!window_info) {
+    return true;
+  }
+
+  // Both CHROME and DEFAULT indicate Chrome style with Chrome bootstrap.
+  return window_info->runtime_style == CEF_RUNTIME_STYLE_CHROME ||
+         window_info->runtime_style == CEF_RUNTIME_STYLE_DEFAULT;
+}
+
+bool CefBrowserCreateParams::IsChromeStyle() const {
+  if (!cef::IsChromeRuntimeEnabled()) {
+    return false;
+  }
+
+  const bool chrome_style_via_window_info = IsChromeStyle(window_info.get());
+
+  if (popup_with_alloy_style_opener) {
+    // Creating a popup where the opener is Alloy style.
+    if (chrome_style_via_window_info &&
+        window_info->runtime_style == CEF_RUNTIME_STYLE_CHROME) {
+      // Only use Chrome style for the popup if the client explicitly sets
+      // CHROME (and not DEFAULT) via CefWindowInfo.runtime_style.
+      return true;
+    }
+    return false;
+  }
+
+  if (browser_view) {
+    // Must match the BrowserView style. GetRuntimeStyle() will not return
+    // DEFAULT.
+    return browser_view->GetRuntimeStyle() == CEF_RUNTIME_STYLE_CHROME;
+  }
+
+  // Chrome style does not support windowless rendering.
+  return chrome_style_via_window_info && !IsWindowless();
+}
+
+bool CefBrowserCreateParams::IsWindowless() const {
+  return window_info && window_info->windowless_rendering_enabled && client &&
+         client->GetRenderHandler().get();
+}
+
+// static
+void CefBrowserCreateParams::InitWindowInfo(CefWindowInfo* window_info,
+                                            CefBrowserHostBase* opener) {
+#if BUILDFLAG(IS_WIN)
+  window_info->SetAsPopup(nullptr, CefString());
+#endif
+
+  if (cef::IsChromeRuntimeEnabled() && opener->IsAlloyStyle()) {
+    // Give the popup the same runtime style as the opener.
+    window_info->runtime_style = CEF_RUNTIME_STYLE_ALLOY;
+  }
+}
+
 void CefBrowserCreateParams::MaybeSetWindowInfo(
-    const CefWindowInfo& new_window_info) {
-  if (!cef::IsChromeRuntimeEnabled() ||
+    const CefWindowInfo& new_window_info,
+    bool allow_alloy_style,
+    bool allow_chrome_style) {
+  if (!cef::IsChromeRuntimeEnabled()) {
+    // Chrome style is not supported wih the Alloy bootstrap.
+    allow_chrome_style = false;
+  }
+
+  if (allow_chrome_style && new_window_info.windowless_rendering_enabled) {
+    // Chrome style is not supported with windowles rendering.
+    allow_chrome_style = false;
+  }
+
+#if BUILDFLAG(IS_MAC)
+  if (allow_chrome_style &&
+      chrome_child_window::HasParentHandle(new_window_info)) {
+    // Chrome style is not supported with native parent on MacOS. See issue
+    // #3294.
+    allow_chrome_style = false;
+  }
+#endif
+
+  DCHECK(allow_alloy_style || allow_chrome_style);
+
+  bool reset_style = false;
+  if (new_window_info.runtime_style == CEF_RUNTIME_STYLE_ALLOY &&
+      !allow_alloy_style) {
+    LOG(ERROR) << "Alloy style is not supported for this browser";
+    reset_style = true;
+  } else if (new_window_info.runtime_style == CEF_RUNTIME_STYLE_CHROME &&
+             !allow_chrome_style) {
+    LOG(ERROR) << "Chrome style is not supported for this browser";
+    reset_style = true;
+  }
+
+  const bool is_chrome_style =
+      allow_chrome_style && IsChromeStyle(&new_window_info);
+  if (!is_chrome_style ||
       chrome_child_window::HasParentHandle(new_window_info)) {
     window_info = std::make_unique<CefWindowInfo>(new_window_info);
+    if (cef::IsChromeRuntimeEnabled() && !allow_chrome_style) {
+      // Only Alloy style is allowed.
+      window_info->runtime_style = CEF_RUNTIME_STYLE_ALLOY;
+    } else if (reset_style) {
+      // Use the default style.
+      window_info->runtime_style = CEF_RUNTIME_STYLE_DEFAULT;
+    }
   }
 }
 
 // static
 CefRefPtr<CefBrowserHostBase> CefBrowserHostBase::Create(
     CefBrowserCreateParams& create_params) {
-  if (cef::IsChromeRuntimeEnabled()) {
+  if (create_params.IsChromeStyle()) {
     if (auto browser =
             chrome_child_window::MaybeCreateChildBrowser(create_params)) {
       return browser.get();