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

gpu/ipc/service/direct_composition_surface_win.cc

Index: gpu/ipc/service/direct_composition_surface_win.cc
diff --git a/gpu/ipc/service/direct_composition_surface_win.cc b/gpu/ipc/service/direct_composition_surface_win.cc
index b0a2af8ef4f683d95531970e0d54ed202b115446..921f0a30459877412875226e4ef681d484665830 100644
--- a/gpu/ipc/service/direct_composition_surface_win.cc
+++ b/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);