Query the preferred readback config in CopyFromBackingStore

content/browser/renderer_host/render_widget_host_view_mac.mm

 // 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/browser/renderer_host/render_widget_host_view_mac.h"
 
 #import <objc/runtime.h>
 #include <QuartzCore/QuartzCore.h>
 
 #include "base/basictypes.h"
@@ skipping 2197 matching lines @@
   ack_params.renderer_id = pending_swap_ack_->renderer_id;
   RenderWidgetHostImpl::AcknowledgeBufferPresent(pending_swap_ack_->route_id,
                                                  pending_swap_ack_->gpu_host_id,
                                                  ack_params);
   if (render_widget_host_)
     render_widget_host_->AcknowledgeSwapBuffersToRenderer();
 
   pending_swap_ack_.reset();
 }
 
+SkBitmap::Config RenderWidgetHostViewMac::PreferredReadbackFormat() {
+  return SkBitmap::kARGB_8888_Config;
+}
+
 }  // namespace content
 
 // RenderWidgetHostViewCocoa ---------------------------------------------------
 
 @implementation RenderWidgetHostViewCocoa
 @synthesize selectedRange = selectedRange_;
 @synthesize suppressNextEscapeKeyUp = suppressNextEscapeKeyUp_;
 @synthesize markedRange = markedRange_;
 
 - (id)initWithRenderWidgetHostViewMac:(RenderWidgetHostViewMac*)r {
@@ skipping 2042 matching lines @@
                                    CGColorGetConstantColor(kCGColorWhite));
     CGContextFillRect(context, clipRect);
   }
 }
 
 - (void)disableRendering {
   renderWidgetHostView_ = NULL;
 }
 
 @end  // implementation SoftwareLayer