aura: Handle released widget when GPU channel gets established

content/browser/compositor/gpu_process_transport_factory.cc

Index: content/browser/compositor/gpu_process_transport_factory.cc
diff --git a/content/browser/compositor/gpu_process_transport_factory.cc b/content/browser/compositor/gpu_process_transport_factory.cc
index b7ed84406a3a9d635384ddda1e3765b703764d6b..2bccfa35bd3d6aaaaaef472523ac65282fe0a56a 100644
--- a/content/browser/compositor/gpu_process_transport_factory.cc
+++ b/content/browser/compositor/gpu_process_transport_factory.cc
@@ -231,7 +231,9 @@ void GpuProcessTransportFactory::EstablishedGpuChannel(
   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)