Query the preferred readback config in CopyFromBackingStore

content/browser/frame_host/render_widget_host_view_guest.cc

 // Copyright 2014 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 "base/bind_helpers.h"
 #include "base/command_line.h"
 #include "base/logging.h"
 #include "base/message_loop/message_loop.h"
 #include "content/browser/browser_plugin/browser_plugin_guest.h"
 #include "content/browser/frame_host/render_widget_host_view_guest.h"
@@ skipping 556 matching lines @@
     ui::GestureRecognizer::Gestures* gestures) {
   if ((gestures == NULL) || gestures->empty())
     return;
   for (ui::GestureRecognizer::Gestures::iterator g_it = gestures->begin();
       g_it != gestures->end();
       ++g_it) {
     ForwardGestureEventToRenderer(*g_it);
   }
 }
 
+SkBitmap::Config RenderWidgetHostViewGuest::PreferredReadbackFormat() {
+  return SkBitmap::kARGB_8888_Config;
+}
 
 }  // namespace content