Implement GpuArcVideoService for arc video accelerator

components/arc/common/video.mojom

Index: components/arc/common/video.mojom
diff --git a/components/arc/common/video.mojom b/components/arc/common/video.mojom
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+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+module arc;
+
+interface VideoHost {
+  // Notifies Chrome a request for ipc channel of video acceleration.
+  OnRequestArcVideoAcceleratorChannel() => (handle channel_handle);
+};
+
+interface VideoInstance {
+  // Establishes full-duplex communication with the host.
+  Init(VideoHost host_ptr);
+};