Wait for GPU to finish before committing first video overlay frame.

The current code to do CopyResource helps in some cases, but with 4k
videos it still may flicker black before the first frame. Waiting for
the GPU commands to execute before the commit seems to help.

BUG=654631
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel

Review-Url: https://codereview.chromium.org/2892123002
Cr-Commit-Position: refs/heads/master@{#473373}

gpu/ipc/service/direct_composition_surface_win.cc

@@ -689,6 +689,17 @@ void DCLayerTree::SwapChainPresenter::PresentToSwapChain(
     base::win::ScopedComPtr<ID3D11DeviceContext> context;
     d3d11_device_->GetImmediateContext(context.GetAddressOf());
     context->CopyResource(dest_texture.Get(), src_texture.Get());
+
+    // Additionally wait for the GPU to finish executing its commands, or
+    // there still may be a black flicker when presenting expensive content
+    // (e.g. 4k video).
+    base::win::ScopedComPtr<IDXGIDevice2> dxgi_device2;
+    hr = d3d11_device_.CopyTo(dxgi_device2.GetAddressOf());
+    DCHECK(SUCCEEDED(hr));
+    base::WaitableEvent event(base::WaitableEvent::ResetPolicy::AUTOMATIC,
+                              base::WaitableEvent::InitialState::NOT_SIGNALED);
+    dxgi_device2->EnqueueSetEvent(event.handle());
+    event.Wait();
   }
 
   swap_chain_->Present(1, 0);