views: Add support for OS and Chrome themes (fixes #3610, fixes #3671)

Controls now respect OS and Chrome themes by default for both Alloy
and Chrome runtimes. Chrome themes (mode and colors) can be configured
using the new CefRequestContext::SetChromeColorScheme method. Individual
theme colors can be overridden using the new CefWindowDelegate::
OnThemeColorsChanged and CefWindow::SetThemeColor methods.

The `--force-light-mode` and `--force-dark-mode` command-line flags are
now respected on all platforms as an override for the OS theme.

The current Chrome theme, if any, will take precedence over the OS theme
when determining light/dark status. On Windows and MacOS the titlebar
color will also be updated to match the light/dark theme.

Testable as follows:
- Run: `cefclient --enable-chrome-runtime` OR
       `cefclient --use-views --persist-user-preferences --cache-path=...`
  - App launches with default OS light/dark theme colors.
  - Change OS dark/light theme under system settings. Notice that theme
    colors change as expected.
  - Right click, select items from the new Theme sub-menu. Notice that
    theme colors behave as expected.
  - Exit and relaunch the app. Notice that the last-used theme colors are
    applied on app restart.
- Add `--background-color=green` to above command-line.
  - Perform the same actions as above. Notice that all controls start
    and remain green throughout (except some icons with Chrome runtime).
- Add `--force-light-mode` or `--force-dark-mode` to above command-line.
  - Perform the same actions as above. Notice that OS dark/light theme
    changes are ignored, but Chrome theme changes work as expected.

patch/patches/light_mode_3534.patch

@@ -31,25 +31,86 @@ index 73d6ad5e9bb36..6c450e79c0f94 100644
    auto& dark_mode_support = GetDarkModeSupport();
    return (dark_mode_support.allow_dark_mode_for_app ||
            dark_mode_support.set_preferred_app_mode) &&
-diff --git ui/native_theme/native_theme_mac.mm ui/native_theme/native_theme_mac.mm
-index d8ff86972911d..0fbafdef0fc26 100644
---- ui/native_theme/native_theme_mac.mm
-+++ ui/native_theme/native_theme_mac.mm
-@@ -51,6 +51,13 @@ bool InvertedColors() {
-   return NSWorkspace.sharedWorkspace.accessibilityDisplayShouldInvertColors;
+diff --git chrome/browser/ui/views/chrome_browser_main_extra_parts_views_linux.cc chrome/browser/ui/views/chrome_browser_main_extra_parts_views_linux.cc
+index 23d0611fdb2b5..81fd1055e926e 100644
+--- chrome/browser/ui/views/chrome_browser_main_extra_parts_views_linux.cc
++++ chrome/browser/ui/views/chrome_browser_main_extra_parts_views_linux.cc
+@@ -61,7 +61,10 @@ void ChromeBrowserMainExtraPartsViewsLinux::ToolkitInitialized() {
+                               linux_ui_theme->GetNativeTheme()->system_theme());
+   }
+ #if defined(USE_DBUS)
+-  dark_mode_manager_ = std::make_unique<ui::DarkModeManagerLinux>();
++  if (!ui::NativeTheme::IsForcedDarkMode() &&
++      !ui::NativeTheme::IsForcedLightMode()) {
++    dark_mode_manager_ = std::make_unique<ui::DarkModeManagerLinux>();
++  }
+ #endif
  }
  
-+bool IsForcedLightMode() {
+diff --git ui/gtk/native_theme_gtk.cc ui/gtk/native_theme_gtk.cc
+index d69b17b004120..5175ea3a785a3 100644
+--- ui/gtk/native_theme_gtk.cc
++++ ui/gtk/native_theme_gtk.cc
+@@ -164,9 +164,11 @@ void NativeThemeGtk::OnThemeChanged(GtkSettings* settings,
+   // have a light variant and aren't affected by the setting.  Because of this,
+   // experimentally check if the theme is dark by checking if the window
+   // background color is dark.
+-  const SkColor window_bg_color = GetBgColor("");
+-  set_use_dark_colors(IsForcedDarkMode() ||
+-                      color_utils::IsDark(window_bg_color));
++  if (!IsForcedLightMode()) {
++    const SkColor window_bg_color = GetBgColor("");
++    set_use_dark_colors(IsForcedDarkMode() ||
++                        color_utils::IsDark(window_bg_color));
++  }
+   set_preferred_color_scheme(CalculatePreferredColorScheme());
+ 
+   // GTK doesn't have a native high contrast setting.  Rather, it's implied by
+diff --git ui/native_theme/native_theme.cc ui/native_theme/native_theme.cc
+index d466e72df7e2c..d0a58289ca291 100644
+--- ui/native_theme/native_theme.cc
++++ ui/native_theme/native_theme.cc
+@@ -143,6 +143,7 @@ void NativeTheme::NotifyOnNativeThemeUpdated() {
+   color_provider_manager.ResetColorProviderCache();
+   for (NativeThemeObserver& observer : native_theme_observers_)
+     observer.OnNativeThemeUpdated(this);
++  color_provider_manager.AfterNativeThemeUpdated();
+ 
+   RecordNumColorProvidersInitializedDuringOnNativeThemeUpdated(
+       color_provider_manager.num_providers_initialized() -
+@@ -276,6 +277,13 @@ bool NativeTheme::IsForcedDarkMode() {
+   return kIsForcedDarkMode;
+ }
+ 
++bool NativeTheme::IsForcedLightMode() {
 +  static bool kIsForcedLightMode =
 +      base::CommandLine::ForCurrentProcess()->HasSwitch(
 +          "force-light-mode");
 +  return kIsForcedLightMode;
 +}
 +
- }  // namespace
+ bool NativeTheme::IsForcedHighContrast() {
+   static bool kIsForcedHighContrast =
+       base::CommandLine::ForCurrentProcess()->HasSwitch(
+diff --git ui/native_theme/native_theme.h ui/native_theme/native_theme.h
+index 3385e9e9d5690..54b69691383bf 100644
+--- ui/native_theme/native_theme.h
++++ ui/native_theme/native_theme.h
+@@ -603,6 +603,9 @@ class NATIVE_THEME_EXPORT NativeTheme {
+   // Whether dark mode is forced via command-line flag.
+   static bool IsForcedDarkMode();
  
- // Helper object to respond to light mode/dark mode changeovers.
-@@ -585,11 +592,15 @@ void NativeThemeMac::PaintSelectedMenuItem(
++  // Whether light mode is forced via command-line flag.
++  static bool IsForcedLightMode();
++
+  protected:
+   explicit NativeTheme(
+       bool should_only_use_dark_colors,
+diff --git ui/native_theme/native_theme_mac.mm ui/native_theme/native_theme_mac.mm
+index d8ff86972911d..c6cc9c70741c9 100644
+--- ui/native_theme/native_theme_mac.mm
++++ ui/native_theme/native_theme_mac.mm
+@@ -585,11 +585,15 @@ void NativeThemeMac::PaintSelectedMenuItem(
  
  void NativeThemeMac::InitializeDarkModeStateAndObserver() {
    __block auto theme = this;