mus: Disable external begin-frame source in the renderer.

content/renderer/gpu/render_widget_compositor.cc

 // Copyright (c) 2013 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.
 
 #include "content/renderer/gpu/render_widget_compositor.h"
 
 #include <stddef.h>
 #include <limits>
 #include <string>
 #include <utility>
@@ skipping 494 matching lines @@
   // Use 1/4th of staging buffers on low-end devices.
   if (base::SysInfo::IsLowEndDevice())
     settings.max_staging_buffer_usage_in_bytes /= 4;
 
   cc::ManagedMemoryPolicy current = settings.memory_policy_;
   settings.memory_policy_ = GetGpuMemoryPolicy(current);
 
   settings.use_cached_picture_raster =
       !cmd.HasSwitch(cc::switches::kDisableCachedPictureRaster);
 
-  if (cmd.HasSwitch(switches::kUseRemoteCompositing))
+  if (cmd.HasSwitch(switches::kUseRemoteCompositing) ||
+      cmd.HasSwitch(switches::kIsRunningInMash))
     settings.use_external_begin_frame_source = false;
 
   return settings;
 }
 
 // static
 cc::ManagedMemoryPolicy RenderWidgetCompositor::GetGpuMemoryPolicy(
     const cc::ManagedMemoryPolicy& policy) {
   cc::ManagedMemoryPolicy actual = policy;
   actual.bytes_limit_when_visible = 0;
@@ skipping 619 matching lines @@
 
   remote_proto_channel_receiver_->OnProtoReceived(std::move(deserialized));
 }
 
 void RenderWidgetCompositor::SetPaintedDeviceScaleFactor(
     float device_scale) {
   layer_tree_host_->SetPaintedDeviceScaleFactor(device_scale);
 }
 
 }  // namespace content