Prevent browser thumbnailer from trying to read from frontbuffer (surface texture) when none exists.

content/browser/renderer_host/render_widget_host_view_aura.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/browser/renderer_host/render_widget_host_view_aura.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/command_line.h"
 #include "base/logging.h"
@@ skipping 314 matching lines @@
 }
 
 void RenderWidgetHostViewAura::Blur() {
   window_->Blur();
 }
 
 bool RenderWidgetHostViewAura::HasFocus() const {
   return window_->HasFocus();
 }
 
+bool RenderWidgetHostViewAura::IsSurfaceAvailableForCopy() const {
+  return current_surface_ != 0;
+}
+
 void RenderWidgetHostViewAura::Show() {
   window_->Show();
 }
 
 void RenderWidgetHostViewAura::Hide() {
   window_->Hide();
 }
 
 bool RenderWidgetHostViewAura::IsShowing() {
   return window_->IsVisible();
@@ skipping 96 matching lines @@
 
 void RenderWidgetHostViewAura::CopyFromCompositingSurface(
     const gfx::Size& size,
     skia::PlatformCanvas* output,
     base::Callback<void(bool)> callback) {
   base::ScopedClosureRunner scoped_callback_runner(base::Bind(callback, false));
   ui::Compositor* compositor = GetCompositor();
   if (!compositor)
     return;
 
+  DCHECK(image_transport_clients_.find(current_surface_) !=
+         image_transport_clients_.end());

[mazda, 2012/05/23 20:06:23]

When this condition holds, |container| is initialized with NULL, so this
function returns as failure before calling GLHelper::CopyTextureTo, right?
I think just returning as failure is appropriate instead of causing CHECK error.

[mmocny, 2012/05/23 20:28:30]

You are right.  The issue was that we expect the existence of a client in the
map to imply !NULL, and so the use of map op[] was causing issues elsewhere. 
Changed this to exit early as you suggest instead.

On 2012/05/23 20:06:23, mazda wrote:

   ImageTransportClient* container = image_transport_clients_[current_surface_];
   if (!container)
     return;
 
   if (!output->initialize(size.width(), size.height(), true))
     return;
 
   ImageTransportFactory* factory = ImageTransportFactory::GetInstance();
   content::GLHelper* gl_helper = factory->GetGLHelper(compositor);
   if (!gl_helper)
@@ skipping 849 matching lines @@
 RenderWidgetHostView* RenderWidgetHostView::CreateViewForWidget(
     RenderWidgetHost* widget) {
   return new RenderWidgetHostViewAura(widget);
 }
 
 // static
 void content::RenderWidgetHostViewPort::GetDefaultScreenInfo(
     WebKit::WebScreenInfo* results) {
   GetScreenInfoForWindow(results, NULL);
 }