Enable WebGL rendering into ImageCHROMIUM, backed by a scanout buffer to enable overlay suppor…

public/platform/WebExternalTextureMailbox.h

 /*
  * Copyright (C) 2013 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 18 matching lines @@
  */
 
 #ifndef WebExternalTextureMailbox_h
 #define WebExternalTextureMailbox_h
 
 namespace blink {
 
 struct WebExternalTextureMailbox {
     signed char name[64];
     unsigned syncPoint;
+    bool allowOverlay;
 
     WebExternalTextureMailbox()
         : syncPoint(0)
+        , allowOverlay(false)
     {
         memset(name, 0, sizeof(name));
     }
 };
 
 inline bool nameEquals(const WebExternalTextureMailbox& a, const WebExternalTextureMailbox& b)
 {
     return !memcmp(a.name, b.name, sizeof(a.name));
 }
 
 } // namespace blink
 
 #endif // WebExternalTextureMailbox_h