Hoist begin frame sources out of scheduler

cc/trees/single_thread_proxy.h

 // 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.
 
 #ifndef CC_TREES_SINGLE_THREAD_PROXY_H_
 #define CC_TREES_SINGLE_THREAD_PROXY_H_
 
 #include <limits>
 
 #include "base/cancelable_callback.h"
@@ skipping 126 matching lines @@
   LayerTreeHostSingleThreadClient* client_;
 
   TaskRunnerProvider* task_runner_provider_;
 
   // Used on the Thread, but checked on main thread during
   // initialization/shutdown.
   scoped_ptr<LayerTreeHostImpl> layer_tree_host_impl_;
   RendererCapabilities renderer_capabilities_for_main_thread_;
 
   // Accessed from both threads.
-  scoped_ptr<BeginFrameSource> external_begin_frame_source_;
+  scoped_ptr<BeginFrameSource> begin_frame_source_;

[Sami, 2016/03/08 19:15:25]

Sorry to latch onto the naming but I would keep this as
external_begin_frame_source_. Otherwise it's not really obvious when this would
be set vs. the synthetic one. WDYT? (same comment for proxy_impl.h)

[enne (OOO), 2016/03/08 21:38:02]

This ends up being either the external one or the throttled one.  Would you
rather I have three better named variables, only one of which is valid?

[Sami, 2016/03/09 14:36:23]

The new design with precise names for all the three alternatives looks pretty
clear to me.

+  scoped_ptr<SyntheticBeginFrameSource> synthetic_frame_source_;

[Sami, 2016/03/08 19:15:25]

nit: synthetic_begin_frame_source_

   scoped_ptr<Scheduler> scheduler_on_impl_thread_;
 
+  base::TimeDelta authoritative_vsync_interval_;
+  base::TimeTicks last_vsync_timebase_;
+
   scoped_ptr<BlockingTaskRunner::CapturePostTasks> commit_blocking_task_runner_;
   bool next_frame_is_newly_committed_frame_;
 
 #if DCHECK_IS_ON()
   bool inside_impl_frame_;
 #endif
   bool inside_draw_;
   bool defer_commits_;
   bool animate_requested_;
   bool commit_requested_;
@@ skipping 72 matching lines @@
  private:
   DebugScopedSetImplThread impl_thread_;
   DebugScopedSetMainThreadBlocked main_thread_blocked_;
 
   DISALLOW_COPY_AND_ASSIGN(DebugScopedSetImplThreadAndMainThreadBlocked);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_SINGLE_THREAD_PROXY_H_