Mozart: Improve tracing and backpressure.

services/gfx/compositor/compositor_engine.h

Index: services/gfx/compositor/compositor_engine.h
diff --git a/services/gfx/compositor/compositor_engine.h b/services/gfx/compositor/compositor_engine.h
index 05c3e8d16c6d95b20a99dd3f03acc722f5f82a74..a1a73293ea7125b057a2fa07d910d13432b4e32e 100644
--- a/services/gfx/compositor/compositor_engine.h
+++ b/services/gfx/compositor/compositor_engine.h
@@ -89,12 +89,16 @@ class CompositorEngine {
   SceneDef::Disposition PresentScene(SceneState* scene_state,
                                      int64_t presentation_time);
 
+  void ComposeRenderer(RendererState* renderer_state,

[mikejurka, 2016/05/19 23:26:19]

Compose/Present/Paint all sound relatively similar--- could you write comments
explaining the differences here?

[jeffbrown, 2016/05/20 01:09:48]

Sure!

+                       const mojo::gfx::composition::FrameInfo& frame_info);
   void PresentRenderer(RendererState* renderer_state,
                        int64_t presentation_time);
-  void SnapshotRenderer(RendererState* renderer_state,
-                        const mojo::gfx::composition::FrameInfo& frame_info);
+  void SnapshotRenderer(RendererState* renderer_state);
   void SnapshotRendererInner(RendererState* renderer_state,
                              std::ostream* block_log);
+  void PaintRenderer(RendererState* renderer_state,
+                     const mojo::gfx::composition::FrameInfo& frame_info,
+                     int64_t composition_time);
   void ScheduleFrameForRenderer(RendererState* renderer_state,
                                 Scheduler::SchedulingMode scheduling_mode);