aura: Handle released widget when GPU channel gets established

content/browser/compositor/gpu_process_transport_factory.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 "content/browser/compositor/gpu_process_transport_factory.h"
 
 #include <string>
 
 #include "base/bind.h"
 #include "base/command_line.h"
@@ skipping 212 matching lines @@
     EstablishedGpuChannel(compositor, create_gpu_output_surface, 0);
   }
 }
 
 void GpuProcessTransportFactory::EstablishedGpuChannel(
     base::WeakPtr<ui::Compositor> compositor,
     bool create_gpu_output_surface,
     int num_attempts) {
   if (!compositor)
     return;
   PerCompositorData* data = per_compositor_data_[compositor.get()];

[piman, 2015/10/20 01:51:49]

Can you use per_compositor_data_.find(compositor.get()), so that you avoid
adding a NULL entry that nothing will clear later (logical leak)?

-  DCHECK(data);
+  // The widget might have been released in the meantime.
+  if (!data)
+    return;
 
   if (num_attempts > kNumRetriesBeforeSoftwareFallback) {
 #if defined(OS_CHROMEOS)
     LOG(FATAL) << "Unable to create a UI graphics context, and cannot use "
                << "software compositing on ChromeOS.";
 #endif
     create_gpu_output_surface = false;
   }
 
   scoped_refptr<ContextProviderCommandBuffer> context_provider;
@@ skipping 388 matching lines @@
   FOR_EACH_OBSERVER(ImageTransportFactoryObserver,
                     observer_list_,
                     OnLostResources());
 
   // Kill things that use the shared context before killing the shared context.
   lost_gl_helper.reset();
   lost_shared_main_thread_contexts  = NULL;
 }
 
 }  // namespace content