Don't crash when a context can't be created for HW video decode.

BUG=139061


Review URL: https://chromiumcodereview.appspot.com/10834019

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@148468 0039d316-1c4b-4281-b951-d872f2087c98

content/renderer/render_thread_impl.cc

@@ -772,6 +772,8 @@ RenderThreadImpl::GetGpuVDAContext3D() {
             this, WebKit::WebGraphicsContext3D::Attributes(),
             GURL("chrome://gpu/RenderThreadImpl::GetGpuVDAContext3D")));
   }
+  if (!gpu_vda_context3d_.get())
+    return base::WeakPtr<WebGraphicsContext3DCommandBufferImpl>();
   return gpu_vda_context3d_->AsWeakPtr();
 }