Implement offscreenCanvas.getContext('webgl') on a worker thread

gpu/ipc/client/command_buffer_proxy_impl.h

Index: gpu/ipc/client/command_buffer_proxy_impl.h
diff --git a/gpu/ipc/client/command_buffer_proxy_impl.h b/gpu/ipc/client/command_buffer_proxy_impl.h
index 203a8a9e791fae2eda4f2724307e15f88cff431c..129a962caa3c8332863195848c666d3af46b729c 100644
--- a/gpu/ipc/client/command_buffer_proxy_impl.h
+++ b/gpu/ipc/client/command_buffer_proxy_impl.h
@@ -102,6 +102,7 @@ class GPU_EXPORT CommandBufferProxyImpl
                                      unsigned usage) override;
   void SignalQuery(uint32_t query, const base::Closure& callback) override;
   void SetLock(base::Lock* lock) override;
+  void DetachFromThread() { lockless_thread_checker_.DetachFromThread(); }
   void EnsureWorkVisible() override;
   gpu::CommandBufferNamespace GetNamespaceID() const override;
   gpu::CommandBufferId GetCommandBufferID() const override;