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]`

patch/patches/chrome_runtime_views.patch

@@ -1107,16 +1107,20 @@ index 325b73a399d3f..9242aed24ef35 100644
    ToolbarView& operator=(const ToolbarView&) = delete;
    ~ToolbarView() override;
 diff --git chrome/browser/ui/web_applications/draggable_region_host_impl.cc chrome/browser/ui/web_applications/draggable_region_host_impl.cc
-index 8980b03f2c945..6e719e0abced7 100644
+index 8980b03f2c945..831f6dd681cb9 100644
 --- chrome/browser/ui/web_applications/draggable_region_host_impl.cc
 +++ chrome/browser/ui/web_applications/draggable_region_host_impl.cc
-@@ -11,6 +11,24 @@
+@@ -11,6 +11,28 @@
  #include "chrome/common/chrome_features.h"
  #include "mojo/public/cpp/bindings/self_owned_receiver.h"
  
 +namespace {
 +
 +bool IsSupported(Browser* browser) {
++  // May be nullptr when running with Alloy style.
++  if (!browser)
++    return false;
++
 +  if (web_app::AppBrowserController::IsWebApp(browser))
 +    return true;
 +
@@ -1135,7 +1139,7 @@ index 8980b03f2c945..6e719e0abced7 100644
  DraggableRegionsHostImpl::DraggableRegionsHostImpl(
      content::RenderFrameHost& render_frame_host,
      mojo::PendingReceiver<chrome::mojom::DraggableRegions> receiver)
-@@ -28,7 +46,7 @@ void DraggableRegionsHostImpl::CreateIfAllowed(
+@@ -28,7 +50,7 @@ void DraggableRegionsHostImpl::CreateIfAllowed(
    auto* browser = chrome::FindBrowserWithTab(web_contents);
  
    // We only want to bind the receiver for PWAs.
@@ -1144,7 +1148,7 @@ index 8980b03f2c945..6e719e0abced7 100644
      return;
  
    // The object is bound to the lifetime of |render_frame_host| and the mojo
-@@ -43,7 +61,7 @@ void DraggableRegionsHostImpl::UpdateDraggableRegions(
+@@ -43,7 +65,7 @@ void DraggableRegionsHostImpl::UpdateDraggableRegions(
    auto* browser = chrome::FindBrowserWithTab(web_contents);
    // When a WebApp browser's WebContents is reparented to a tabbed browser, a
    // draggable regions update may race with the reparenting logic.
@@ -1153,7 +1157,7 @@ index 8980b03f2c945..6e719e0abced7 100644
      return;
  
    SkRegion sk_region;
-@@ -56,5 +74,12 @@ void DraggableRegionsHostImpl::UpdateDraggableRegions(
+@@ -56,5 +78,12 @@ void DraggableRegionsHostImpl::UpdateDraggableRegions(
    }
  
    auto* app_browser_controller = browser->app_controller();