Allow DrawingBuffer to present to a bitmap.

public/platform/WebGraphicsContext3D.h

 /*
  * 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:
  *
  *     * 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 170 matching lines @@
     // GL_CHROMIUM_discard_backbuffer - controls allocation/deallocation of the back buffer.
     virtual void discardBackbufferCHROMIUM() { }
     virtual void ensureBackbufferCHROMIUM() { }
 
     virtual unsigned insertSyncPoint() { return 0; }
     virtual void waitSyncPoint(unsigned) { }
     // This call passes ownership of the WebGraphicsSyncPointCallback to the
     // WebGraphicsContext3D implementation.
     virtual void signalSyncPoint(unsigned syncPoint, WebGraphicsSyncPointCallback* callback) { delete callback; }
 
-    // Helper for software compositing path. Reads back the frame buffer into
-    // the memory region pointed to by "pixels" with size "bufferSize". It is
-    // expected that the storage for "pixels" covers (4 * width * height) bytes.
-    // The RGBA channels are packed into "pixels" using SkBitmap's byte
-    // ordering. Returns true on success.
-    virtual bool readBackFramebuffer(unsigned char* pixels, size_t bufferSize, WebGLId framebuffer, int width, int height) = 0;
-
     // Copies the contents of the off-screen render target used by the WebGL
     // context to the corresponding texture used by the compositor.
     virtual void prepareTexture() = 0;
 
     // GL_CHROMIUM_post_sub_buffer - Copies part of the back buffer to the front buffer.
     virtual void postSubBufferCHROMIUM(int x, int y, int width, int height) = 0;
 
     // Synthesizes an OpenGL error which will be returned from a
     // later call to getError. This is used to emulate OpenGL ES
     // 2.0 behavior on the desktop and to enforce additional error
@@ skipping 281 matching lines @@
     virtual void unmapImageCHROMIUM(WGC3Duint imageId) { }
 
 protected:
     virtual GrGLInterface* onCreateGrGLInterface() { return 0; }
 
 };
 
 } // namespace WebKit
 
 #endif