Use explicit flush for ArcVideoAccelerator.

chrome/gpu/gpu_arc_video_service.cc

Index: chrome/gpu/gpu_arc_video_service.cc
diff --git a/chrome/gpu/gpu_arc_video_service.cc b/chrome/gpu/gpu_arc_video_service.cc
index 0ab69c736c3dbaebe6a5650be310538dacd0cb11..e17491558121ec7d2e04c1cab1bd3a66b23b17dc 100644
--- a/chrome/gpu/gpu_arc_video_service.cc
+++ b/chrome/gpu/gpu_arc_video_service.cc
@@ -152,6 +152,11 @@ class GpuArcVideoService::AcceleratorStub
     client_->OnResetDone();
   }
 
+  void OnFlushDone() override {
+    DVLOG(2) << "OnFlushDone";
+    client_->OnFlushDone();
+  }
+
   void OnOutputFormatChanged(const VideoFormat& format) override {
     DVLOG(2) << "OnOutputFormatChanged";
     client_->OnOutputFormatChanged(::arc::mojom::VideoFormat::From(format));
@@ -213,6 +218,8 @@ class GpuArcVideoService::AcceleratorStub
 
   void Reset() override { accelerator_->Reset(); }
 
+  void Flush() override { accelerator_->Flush(); }
+
  private:
   base::ThreadChecker thread_checker_;
   GpuArcVideoService* const owner_;