Allow DrawingBuffer to present to a bitmap.

Source/core/platform/graphics/chromium/Canvas2DLayerBridge.cpp

 /*
  * Copyright (C) 2012 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:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 152 matching lines @@
     }
     return 0;
 #endif  // !ENABLE(CANVAS_USES_MAILBOX)
 }
 
 WebGraphicsContext3D* Canvas2DLayerBridge::context()
 {
     return m_context->webContext();
 }
 
-bool Canvas2DLayerBridge::prepareMailbox(WebKit::WebExternalTextureMailbox* outMailbox)
+bool Canvas2DLayerBridge::prepareMailbox(WebKit::WebExternalTextureMailbox* outMailbox, WebKit::WebExternalBitmap* bitmap)
 {
 #if ENABLE(CANVAS_USES_MAILBOX)
+    ASSERT(!bitmap);
     // Release to skia textures that were previouosly released by the
     // compositor. We do this before acquiring the next snapshot in
     // order to cap maximum gpu memory consumption.
     m_context->makeContextCurrent();
     Vector<MailboxInfo>::iterator mailboxInfo;
     for (mailboxInfo = m_mailboxes.begin(); mailboxInfo < m_mailboxes.end(); mailboxInfo++) {
         if (mailboxInfo->m_status == MailboxReleased) {
             if (mailboxInfo->m_mailbox.syncPoint) {
                 context()->waitSyncPoint(mailboxInfo->m_mailbox.syncPoint);
                 mailboxInfo->m_mailbox.syncPoint = 0;
@@ skipping 114 matching lines @@
     // This copy constructor should only be used for Vector reallocation
     // Assuming 'other' is to be destroyed, we swap m_image ownership
     // rather than do a refcount dance.
     memcpy(&m_mailbox, &other.m_mailbox, sizeof(m_mailbox));
     m_image.swap(const_cast<SkAutoTUnref<SkImage>*>(&other.m_image));
     m_status = other.m_status;
 }
 #endif
 
 }