Adds BeginFrameControl via DevTools.

ui/compositor/compositor.cc

Index: ui/compositor/compositor.cc
diff --git a/ui/compositor/compositor.cc b/ui/compositor/compositor.cc
index 63f72bc6178b815d9008fb0daff580c3ae1db9fd..a431a412ceae9657bb0529093256bdb44fe06e85 100644
--- a/ui/compositor/compositor.cc
+++ b/ui/compositor/compositor.cc
@@ -374,6 +374,11 @@ void Compositor::SetDisplayVSyncParameters(base::TimeTicks timebase,
   vsync_manager_->UpdateVSyncParameters(timebase, interval);
 }
 
+void Compositor::SwapBeginFrameSource(
+    std::unique_ptr<cc::BeginFrameSource>* begin_frame_source) {
+  context_factory_->SwapBeginFrameSource(this, begin_frame_source);
+}
+
 void Compositor::SetAcceleratedWidget(gfx::AcceleratedWidget widget) {
   // This function should only get called once.
   DCHECK(!widget_valid_);