SkiaOutputdeviceBufferQueue: kick off next frame earlier

PageFlipComplete() is not trivial, so call FinishSwapBuffers()
before it to kick off next frame in viz thread earlier, and compositor
will have more time budget to render the next frame.

Bug: None
Change-Id: Ie6e0f87d75d81b405447757585ec291887ca0063
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2057043
Commit-Queue: Vasiliy Telezhnikov <vasilyt@chromium.org>
Auto-Submit: Peng Huang <penghuang@chromium.org>
Reviewed-by: Vasiliy Telezhnikov <vasilyt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#741430}

components/viz/service/display_embedder/skia_output_device_buffer_queue.cc

@@ -521,8 +521,8 @@ void SkiaOutputDeviceBufferQueue::DoFinishSwapBuffers(
     std::unique_ptr<gfx::GpuFence> gpu_fence) {
   DCHECK(!gpu_fence);
 
-  PageFlipComplete(image.get());
   FinishSwapBuffers(result, size, latency_info);
+  PageFlipComplete(image.get());
 }
 
 bool SkiaOutputDeviceBufferQueue::Reshape(const gfx::Size& size,