Don't try to set context callback if the context failed to be created.

content/renderer/render_thread_impl.cc

Index: content/renderer/render_thread_impl.cc
diff --git a/content/renderer/render_thread_impl.cc b/content/renderer/render_thread_impl.cc
index 6bdc9b64313cbdfb162a36c645e66e1053d0585a..b5727f3b4dba010f3264460e5f4149d6ae93a6d6 100644
--- a/content/renderer/render_thread_impl.cc
+++ b/content/renderer/render_thread_impl.cc
@@ -793,7 +793,8 @@ RenderThreadImpl::GetGpuVDAContext3D() {
         WebGraphicsContext3DCommandBufferImpl::CreateOffscreenContext(
             this, WebKit::WebGraphicsContext3D::Attributes(),
             GURL("chrome://gpu/RenderThreadImpl::GetGpuVDAContext3D")));
-    gpu_vda_context3d_->setContextLostCallback(context_lost_cb_.get());
+    if (gpu_vda_context3d_.get())
+      gpu_vda_context3d_->setContextLostCallback(context_lost_cb_.get());
   }
   return gpu_vda_context3d_.get();
 }