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]`

tests/ceftests/test_handler.h

@@ -219,6 +219,8 @@ class TestHandler : public CefClient,
   }
 
   std::string debug_string_prefix() const { return debug_string_prefix_; }
+  bool use_alloy_style_browser() const { return use_alloy_style_browser_; }
+  bool use_alloy_style_window() const { return use_alloy_style_window_; }
 
  protected:
   // Indicate that test setup is complete. Only used in combination with a
@@ -277,11 +279,19 @@ class TestHandler : public CefClient,
   // Call OnTestTimeout() after the specified amount of time.
   void SetTestTimeout(int timeout_ms = 5000, bool treat_as_error = true);
 
-  // Call prior to CreateBrowser() to configure whether browsers will be created
-  // as Views-hosted. Defaults to false unless the `--use-views` command-line
-  // flag is specified.
+  // Call prior to CreateBrowser() to configure whether browsers and windows
+  // will be created as Views-hosted. Defaults to false unless the `--use-views`
+  // command-line flag is specified.
   void SetUseViews(bool use_views);
 
+  // Call prior to CreateBrowser() to configure whether browsers (and windows
+  // with Views) will be created as Alloy style or Chrome style. Alloy style is
+  // always used with the Alloy runtime and optional with the Chrome runtime.
+  // Defaults to false for the Chrome runtime unless the
+  // `--use-alloy-style` command-line flag is specified.
+  void SetUseAlloyStyle(bool use_alloy_style_browser,
+                        bool use_alloy_style_window);
+
   // Returns the single UIThreadHelper instance, creating it if necessary. Must
   // be called on the UI thread.
   UIThreadHelper* GetUIThreadHelper();
@@ -308,6 +318,8 @@ class TestHandler : public CefClient,
   bool completion_state_owned_;
 
   bool use_views_;
+  bool use_alloy_style_browser_;
+  bool use_alloy_style_window_;
 
   // Map of browser ID to browser object. Only accessed on the UI thread.
   BrowserMap browser_map_;