[blink] Support (semi-)transparent background colors in WebView/Frame.

third_party/WebKit/Source/web/FullscreenController.h

Index: third_party/WebKit/Source/web/FullscreenController.h
diff --git a/third_party/WebKit/Source/web/FullscreenController.h b/third_party/WebKit/Source/web/FullscreenController.h
index a4bd8d9658075300ab1fa6524cc35c06df25b385..1a66c28718b3b95d996deda9680400e7e3052394 100644
--- a/third_party/WebKit/Source/web/FullscreenController.h
+++ b/third_party/WebKit/Source/web/FullscreenController.h
@@ -31,9 +31,11 @@
 #ifndef FullscreenController_h
 #define FullscreenController_h
 
+#include <memory>
+
 #include "platform/geometry/FloatPoint.h"
 #include "platform/geometry/IntSize.h"
-#include <memory>
+#include "platform/graphics/Color.h"
 
 namespace blink {
 
@@ -71,6 +73,7 @@ class FullscreenController {
 
  private:
   void updatePageScaleConstraints(bool removeConstraints);
+  void restoreBackgroundColorOverride();
 
   WebViewImpl* m_webViewImpl;
 
@@ -94,6 +97,8 @@ class FullscreenController {
   float m_initialPageScaleFactor = 0.0f;
   IntSize m_initialScrollOffset;
   FloatPoint m_initialVisualViewportOffset;
+  bool m_initialBackgroundColorOverrideEnabled = false;
+  RGBA32 m_initialBackgroundColorOverride = Color::transparent;
 };
 
 }  // namespace blink