Remove the forceCompositingMode setting.

public/web/WebWidget.h

 /*
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 78 matching lines @@
     // Called to update imperative animation state. This should be called before
     // paint, although the client can rate-limit these calls.
     virtual void animate(double monotonicFrameBeginTime) { }
 
     // Called to layout the WebWidget. This MUST be called before Paint,
     // and it may result in calls to WebWidgetClient::didInvalidateRect.
     virtual void layout() { }
 
     // Called to toggle the WebWidget in or out of force compositing mode. This
     // should be called before paint.
+    // FIXME: Remove this once WebPopuMenuImpl stops overriding it. crbug.com/378029
     virtual void enterForceCompositingMode(bool enter) { }
 
     // Called to paint the rectangular region within the WebWidget
     // onto the specified canvas at (viewPort.x,viewPort.y). You MUST call
     // Layout before calling this method. It is okay to call paint
     // multiple times once layout has been called, assuming no other
     // changes are made to the WebWidget (e.g., once events are
     // processed, it should be assumed that another call to layout is
     // warranted before painting again).
     virtual void paint(WebCanvas*, const WebRect& viewPort) { }
@@ skipping 138 matching lines @@
     // content.
     virtual WebColor backgroundColor() const { return 0xFFFFFFFF; /* SK_ColorWHITE */ }
 
 protected:
     ~WebWidget() { }
 };
 
 } // namespace blink
 
 #endif