cc: Make async readback path use async glRreadPixels.

content/common/gpu/client/gl_helper.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/common/gpu/client/gl_helper.h"
 
 #include <queue>
 
 #include "base/bind.h"
 #include "base/debug/trace_event.h"
@@ skipping 537 matching lines @@
                                  0);
   request->buffer = context_->createBuffer();
   context_->bindBuffer(GL_PIXEL_PACK_TRANSFER_BUFFER_CHROMIUM,
                        request->buffer);
   context_->bufferData(GL_PIXEL_PACK_TRANSFER_BUFFER_CHROMIUM,
                        4 * size.GetArea(),
                        NULL,
                        GL_STREAM_READ);
 
   context_->readPixels(0, 0, size.width(), size.height(),
-                       GL_RGBA, GL_UNSIGNED_BYTE, 0);
+                       GL_RGBA, GL_UNSIGNED_BYTE, NULL);
   context_->bindBuffer(GL_PIXEL_PACK_TRANSFER_BUFFER_CHROMIUM, 0);
   context_->GetCommandBufferProxy()->SignalSyncPoint(
       context_->insertSyncPoint(),
       base::Bind(&CopyTextureToImpl::ReadbackDone, AsWeakPtr(), request));
 }
 
 void GLHelper::CopyTextureToImpl::ReadbackTextureSync(WebGLId texture,
                                                       const gfx::Rect& src_rect,
                                                       unsigned char* out) {
   ScopedFramebuffer dst_framebuffer(context_, context_->createFramebuffer());
@@ skipping 170 matching lines @@
       context_->copyTexSubImage2D(GL_TEXTURE_2D, 0,
                                   rect.x(), rect.y(),
                                   rect.x(), rect.y(),
                                   rect.width(), rect.height());
     }
     context_->flush();
   }
 }
 
 }  // namespace content