cc: Make async readback path use async glRreadPixels.

cc/output/software_renderer.cc

 // Copyright 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 "cc/output/software_renderer.h"
 
 #include "base/debug/trace_event.h"
 #include "cc/base/math_util.h"
 #include "cc/output/compositor_frame.h"
 #include "cc/output/compositor_frame_ack.h"
@@ skipping 387 matching lines @@
 #ifdef NDEBUG
   current_paint_.setColor(SK_ColorWHITE);
 #else
   current_paint_.setColor(SK_ColorMAGENTA);
 #endif
   current_paint_.setAlpha(quad->opacity() * 255);
   current_canvas_->drawRect(gfx::RectFToSkRect(QuadVertexRect()),
                             current_paint_);
 }
 
-void SoftwareRenderer::CopyCurrentRenderPassToBitmap(DrawingFrame* frame,
-                                                     SkBitmap* bitmap) {
+void SoftwareRenderer::CopyCurrentRenderPassToBitmap(
+    DrawingFrame* frame,
+    const CopyRenderPassCallback& callback) {
   gfx::Size render_pass_size = frame->current_render_pass->output_rect.size();
+
+  scoped_ptr<SkBitmap> bitmap(new SkBitmap);
   bitmap->setConfig(SkBitmap::kARGB_8888_Config,
                     render_pass_size.width(),
                     render_pass_size.height());
-  current_canvas_->readPixels(bitmap, 0, 0);
+  current_canvas_->readPixels(bitmap.get(), 0, 0);
+
+  callback.Run(bitmap.Pass());
 }
 
 void SoftwareRenderer::GetFramebufferPixels(void* pixels, gfx::Rect rect) {
   TRACE_EVENT0("cc", "SoftwareRenderer::GetFramebufferPixels");
   SkBitmap subset_bitmap;
   output_device_->CopyToBitmap(rect, &subset_bitmap);
   subset_bitmap.copyPixelsTo(pixels,
                              4 * rect.width() * rect.height(),
                              4 * rect.width());
 }
 
 void SoftwareRenderer::SetVisible(bool visible) {
   if (visible_ == visible)
     return;
   visible_ = visible;
 }
 
 }  // namespace cc