[wip] hack to use synthetic bfs for browser compositor

cc/trees/single_thread_proxy.cc

 // Copyright 2011 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 "cc/trees/single_thread_proxy.h"
 
 #include "base/auto_reset.h"
 #include "base/memory/ptr_util.h"
 #include "base/profiler/scoped_tracker.h"
 #include "base/trace_event/trace_event.h"
@@ skipping 398 matching lines @@
     // the output surface if already in BEGIN_IMPL_FRAME_STATE_IDLE.
     layer_tree_host_->DidLoseCompositorFrameSink();
   }
   single_thread_client_->DidLoseCompositorFrameSink();
   if (scheduler_on_impl_thread_)
     scheduler_on_impl_thread_->DidLoseCompositorFrameSink();
   compositor_frame_sink_lost_ = true;
 }
 
 void SingleThreadProxy::SetBeginFrameSource(BeginFrameSource* source) {
-  if (scheduler_on_impl_thread_)
-    scheduler_on_impl_thread_->SetBeginFrameSource(source);
+  if (!synthetic_begin_frame_source_) {
+    synthetic_begin_frame_source_.reset(
+        new DelayBasedBeginFrameSource(base::MakeUnique<DelayBasedTimeSource>(
+            task_runner_provider_->MainThreadTaskRunner())));
+  }
+  if (scheduler_on_impl_thread_) {
+    scheduler_on_impl_thread_->SetBeginFrameSource(
+        synthetic_begin_frame_source_.get());
+  }
 }
 
 void SingleThreadProxy::DidReceiveCompositorFrameAckOnImplThread() {
   TRACE_EVENT0("cc,benchmark",
                "SingleThreadProxy::DidReceiveCompositorFrameAckOnImplThread");
   if (scheduler_on_impl_thread_)
     scheduler_on_impl_thread_->DidReceiveCompositorFrameAck();
   layer_tree_host_->DidReceiveCompositorFrameAck();
 }
 
@@ skipping 313 matching lines @@
 void SingleThreadProxy::DidFinishImplFrame() {
   layer_tree_host_impl_->DidFinishImplFrame();
 #if DCHECK_IS_ON()
   DCHECK(inside_impl_frame_)
       << "DidFinishImplFrame called while not inside an impl frame!";
   inside_impl_frame_ = false;
 #endif
 }
 
 }  // namespace cc