Hook up ui::Compositor to Display's BeginFrameSource

cc/surfaces/display_scheduler.cc

Index: cc/surfaces/display_scheduler.cc
diff --git a/cc/surfaces/display_scheduler.cc b/cc/surfaces/display_scheduler.cc
index 28f780862bc10c93388c09b76d6c45f93556fc51..7bbaa09ff69855166cf6efa06ab600dd05f20300 100644
--- a/cc/surfaces/display_scheduler.cc
+++ b/cc/surfaces/display_scheduler.cc
@@ -15,7 +15,8 @@ namespace cc {
 DisplayScheduler::DisplayScheduler(DisplaySchedulerClient* client,
                                    BeginFrameSource* begin_frame_source,
                                    base::SingleThreadTaskRunner* task_runner,
-                                   int max_pending_swaps)
+                                   int max_pending_swaps,
+                                   const RendererSettings& settings)
     : client_(client),
       begin_frame_source_(begin_frame_source),
       task_runner_(task_runner),
@@ -34,9 +35,14 @@ DisplayScheduler::DisplayScheduler(DisplaySchedulerClient* client,
   begin_frame_deadline_closure_ = base::Bind(
       &DisplayScheduler::OnBeginFrameDeadline, weak_ptr_factory_.GetWeakPtr());
 
-  // TODO(tansell): Set this to something useful.
-  begin_frame_source_for_children_ = SyntheticBeginFrameSource::Create(
-      task_runner, BeginFrameArgs::DefaultInterval());
+  if (settings.disable_display_vsync) {

[enne (OOO), 2016/03/28 21:43:27]

I like the way this worked out, in terms of the DisplayScheduler making the
decision here about BeginFrameSource.

[sunnyps, 2016/03/28 23:09:48]

It feels like Display or BrowserCompositorOutputSurface should decide this. That
way we don't need an UpdateSchedulerBFS method or pass RendererSettings here.
But I'm OK with this approach too.

[enne (OOO), 2016/03/29 20:39:52]

I'll make Display do it, because Display already has the renderer settings.  I
don't know how this change will jive with a future world where DisplayScheduler
throttles slow renderers when vsync is disabled, but it shouldn't be hard to
solve that when we get there.

+    unthrottled_begin_frame_source_ =
+        BackToBackBeginFrameSource::Create(task_runner);
+    begin_frame_source_ = unthrottled_begin_frame_source_.get();
+  }
+
+  // TODO(enne): For now, this is always the same, so just set initially.
+  client_->UpdateSchedulerBeginFrameSource(begin_frame_source_);
 }
 
 DisplayScheduler::~DisplayScheduler() {