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

third_party/WebKit/public/platform/WebLayerTreeView.h

Index: third_party/WebKit/public/platform/WebLayerTreeView.h
diff --git a/third_party/WebKit/public/platform/WebLayerTreeView.h b/third_party/WebKit/public/platform/WebLayerTreeView.h
index bc913cb6a50607658ae6ab00a15ac5642cd5b9e5..a00ce584eae3a4e5a813b379d29482e97210fc88 100644
--- a/third_party/WebKit/public/platform/WebLayerTreeView.h
+++ b/third_party/WebKit/public/platform/WebLayerTreeView.h
@@ -71,9 +71,6 @@ class WebLayerTreeView {
   // Sets the background color for the viewport.
   virtual void setBackgroundColor(WebColor) {}
 
-  // Sets the background transparency for the viewport. The default is 'false'.
-  virtual void setHasTransparentBackground(bool) {}
-
   // Sets whether this view is visible. In threaded mode, a view that is not
   // visible will not composite or trigger updateAnimations() or layout() calls
   // until it becomes visible.