Hook up ui::Compositor to Display's BeginFrameSource

cc/surfaces/display_scheduler.h

Index: cc/surfaces/display_scheduler.h
diff --git a/cc/surfaces/display_scheduler.h b/cc/surfaces/display_scheduler.h
index cd4b5db38789a077c93908202d736e78c51bc5c9..fd868b8d2411bb558dc8d3089d0482a084e5beeb 100644
--- a/cc/surfaces/display_scheduler.h
+++ b/cc/surfaces/display_scheduler.h
@@ -11,6 +11,7 @@
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/single_thread_task_runner.h"
+#include "cc/output/renderer_settings.h"
 #include "cc/scheduler/begin_frame_source.h"
 #include "cc/surfaces/surface_id.h"
 #include "cc/surfaces/surfaces_export.h"
@@ -50,10 +51,6 @@ class CC_SURFACES_EXPORT DisplayScheduler : public BeginFrameObserverBase {
   bool OnBeginFrameDerivedImpl(const BeginFrameArgs& args) override;
   void OnBeginFrameSourcePausedChanged(bool paused) override;
 
-  BeginFrameSource* begin_frame_source_for_children() {
-    return begin_frame_source_for_children_.get();
-  }
-
  protected:
   base::TimeTicks DesiredBeginFrameDeadlineTime();
   virtual void ScheduleBeginFrameDeadline();
@@ -70,9 +67,6 @@ class CC_SURFACES_EXPORT DisplayScheduler : public BeginFrameObserverBase {
   base::CancelableClosure begin_frame_deadline_task_;
   base::TimeTicks begin_frame_deadline_task_time_;
 
-  // TODO(tansell): Set this to something useful.
-  std::unique_ptr<BeginFrameSource> begin_frame_source_for_children_;
-
   bool output_surface_lost_;
   bool root_surface_resources_locked_;