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.

include/capi/views/cef_view_capi.h

@@ -33,7 +33,7 @@
 // by hand. See the translator.README.txt file in the tools directory for
 // more information.
 //
-// $hash=0ea5c2c5c1a8e8349f199a46642631be0c1bfb6b$
+// $hash=08f13de764f30261616372dfffb7f97c57957f73$
 //
 
 #ifndef CEF_INCLUDE_CAPI_VIEWS_CEF_VIEW_CAPI_H_
@@ -339,18 +339,29 @@ typedef struct _cef_view_t {
 
   ///
   /// Sets the background color for this View. The background color will be
-  /// automatically reset if the current theme changes. See
-  /// cef_view_delegate_t::OnThemeChanged for related documentation.
+  /// automatically reset when cef_view_delegate_t::OnThemeChanged is called.
   ///
   void(CEF_CALLBACK* set_background_color)(struct _cef_view_t* self,
                                            cef_color_t color);
 
   ///
-  /// Returns the background color for this View. If the background color has
-  /// not been explicitly set then the current theme color will be returned.
+  /// Returns the background color for this View. If the background color is
+  /// unset then the current `GetThemeColor(CEF_ColorPrimaryBackground)` value
+  /// will be returned. If this View belongs to an overlay (created with
+  /// cef_window_t::AddOverlayView), and the background color is unset, then a
+  /// value of transparent (0) will be returned.
   ///
   cef_color_t(CEF_CALLBACK* get_background_color)(struct _cef_view_t* self);
 
+  ///
+  /// Returns the current theme color associated with |color_id|, or the
+  /// placeholder color (red) if unset. See cef_color_ids.h for standard ID
+  /// values. Standard colors can be overridden and custom colors can be added
+  /// using cef_window_t::SetThemeColor.
+  ///
+  cef_color_t(CEF_CALLBACK* get_theme_color)(struct _cef_view_t* self,
+                                             int color_id);
+
   ///
   /// Convert |point| from this View's coordinate system to DIP screen
   /// coordinates. This View must belong to a Window when calling this function.

include/capi/views/cef_view_delegate_capi.h

@@ -33,7 +33,7 @@
 // by hand. See the translator.README.txt file in the tools directory for
 // more information.
 //
-// $hash=d3624baa94bb722c48880b4319f5d5e8035eaa46$
+// $hash=0f562c026f64ca19a32834dcc1e1cd3a98be2f1f$
 //
 
 #ifndef CEF_INCLUDE_CAPI_VIEWS_CEF_VIEW_DELEGATE_CAPI_H_
@@ -143,11 +143,22 @@ typedef struct _cef_view_delegate_t {
 
   ///
   /// Called when the theme for |view| has changed, after the new theme colors
-  /// have already been applied. This will be called at least one time when
-  /// |view| is added to a parent View. Further theme changes can be disabled by
-  /// passing the `--force-dark-mode` or `--force-light-mode` command-line flag.
-  /// Optionally use this callback to override the new theme colors by calling
-  /// the appropriate cef_view_t functions (SetBackgroundColor, etc).
+  /// have already been applied. Views are notified via the component hierarchy
+  /// in depth-first reverse order (children before parents).
+  ///
+  /// This will be called in the following cases:
+  ///
+  /// 1. When |view|, or a parent of |view|, is added to a Window. 2. When the
+  /// native/OS or Chrome theme changes for the Window that contains
+  ///    |view|. See CefWindowDelegate::OnThemeColorsChanged documentation.
+  /// 3. When the client explicitly calls cef_window_t::ThemeChanged on the
+  /// Window
+  ///    that contains |view|.
+  ///
+  /// Optionally use this callback to override the new per-View theme colors by
+  /// calling cef_view_t::SetBackgroundColor or the appropriate component-
+  /// specific function. See cef_window_t::SetThemeColor documentation for how
+  /// to customize additional Window theme colors.
   ///
   void(CEF_CALLBACK* on_theme_changed)(struct _cef_view_delegate_t* self,
                                        struct _cef_view_t* view);

include/capi/views/cef_window_capi.h

@@ -33,7 +33,7 @@
 // by hand. See the translator.README.txt file in the tools directory for
 // more information.
 //
-// $hash=dbe89dfdd14eb114e3f2d16fbfc55624bb91e7ce$
+// $hash=2abb3759a22a95ffc0207f0538c645a74a5030c6$
 //
 
 #ifndef CEF_INCLUDE_CAPI_VIEWS_CEF_WINDOW_CAPI_H_
@@ -364,6 +364,43 @@ typedef struct _cef_window_t {
   /// Remove all keyboard accelerators.
   ///
   void(CEF_CALLBACK* remove_all_accelerators)(struct _cef_window_t* self);
+
+  ///
+  /// Override a standard theme color or add a custom color associated with
+  /// |color_id|. See cef_color_ids.h for standard ID values. Recommended usage
+  /// is as follows:
+  ///
+  /// 1. Customize the default native/OS theme by calling SetThemeColor before
+  ///    showing the first Window. When done setting colors call
+  ///    CefWindow::ThemeChanged to trigger CefViewDelegate::OnThemeChanged
+  ///    notifications.
+  /// 2. Customize the current native/OS or Chrome theme after it changes by
+  ///    calling SetThemeColor from the CefWindowDelegate::OnThemeColorsChanged
+  ///    callback. CefViewDelegate::OnThemeChanged notifications will then be
+  ///    triggered automatically.
+  ///
+  /// The configured color will be available immediately via
+  /// cef_view_t::GetThemeColor and will be applied to each View in this
+  /// Window's component hierarchy when cef_view_delegate_t::OnThemeChanged is
+  /// called. See OnThemeColorsChanged documentation for additional details.
+  ///
+  /// Clients wishing to add custom colors should use |color_id| values >=
+  /// CEF_ChromeColorsEnd.
+  ///
+  void(CEF_CALLBACK* set_theme_color)(struct _cef_window_t* self,
+                                      int color_id,
+                                      cef_color_t color);
+
+  ///
+  /// Trigger cef_view_delegate_t::OnThemeChanged callbacks for each View in
+  /// this Window's component hierarchy. Unlike a native/OS or Chrome theme
+  /// change this function does not reset theme colors to standard values and
+  /// does not result in a call to cef_window_delegate_t::OnThemeColorsChanged.
+  ///
+  /// Do not call this function from cef_window_delegate_t::OnThemeColorsChanged
+  /// or cef_view_delegate_t::OnThemeChanged.
+  ///
+  void(CEF_CALLBACK* theme_changed)(struct _cef_window_t* self);
 } cef_window_t;
 
 ///

include/capi/views/cef_window_delegate_capi.h

@@ -33,7 +33,7 @@
 // by hand. See the translator.README.txt file in the tools directory for
 // more information.
 //
-// $hash=c1c2705cdef7d9189557b57531dc2d53e9f68d0c$
+// $hash=b292cdf6e293dfd42c30ea9189b2a8a2ed77ba7a$
 //
 
 #ifndef CEF_INCLUDE_CAPI_VIEWS_CEF_WINDOW_DELEGATE_CAPI_H_
@@ -224,6 +224,43 @@ typedef struct _cef_window_delegate_t {
   int(CEF_CALLBACK* on_key_event)(struct _cef_window_delegate_t* self,
                                   struct _cef_window_t* window,
                                   const cef_key_event_t* event);
+
+  ///
+  /// Called after the native/OS or Chrome theme for |window| has changed.
+  /// |chrome_theme| will be true (1) if the notification is for a Chrome theme.
+  ///
+  /// Native/OS theme colors are configured globally and do not need to be
+  /// customized for each Window individually. An example of a native/OS theme
+  /// change that triggers this callback is when the user switches between dark
+  /// and light mode during application lifespan. Native/OS theme changes can be
+  /// disabled by passing the `--force-dark-mode` or `--force-light-mode`
+  /// command-line flag.
+  ///
+  /// Chrome theme colors will be applied and this callback will be triggered
+  /// if/when a BrowserView is added to the Window's component hierarchy. Chrome
+  /// theme colors can be configured on a per-RequestContext basis using
+  /// cef_request_context_t::SetChromeColorScheme or (Chrome runtime only) by
+  /// visiting chrome://settings/manageProfile. Any theme changes using those
+  /// mechanisms will also trigger this callback. Chrome theme colors will be
+  /// persisted and restored from disk cache with the Chrome runtime, and with
+  /// the Alloy runtime if persist_user_preferences is set to true (1) via
+  /// CefSettings or cef_request_context_tSettings.
+  ///
+  /// This callback is not triggered on Window creation so clients that wish to
+  /// customize the initial native/OS theme must call
+  /// cef_window_t::SetThemeColor and cef_window_t::ThemeChanged before showing
+  /// the first Window.
+  ///
+  /// Theme colors will be reset to standard values before this callback is
+  /// called for the first affected Window. Call cef_window_t::SetThemeColor
+  /// from inside this callback to override a standard color or add a custom
+  /// color. cef_view_delegate_t::OnThemeChanged will be called after this
+  /// callback for the complete |window| component hierarchy.
+  ///
+  void(CEF_CALLBACK* on_theme_colors_changed)(
+      struct _cef_window_delegate_t* self,
+      struct _cef_window_t* window,
+      int chrome_theme);
 } cef_window_delegate_t;
 
 #ifdef __cplusplus