[animations] Adds metrics for jank on selected layer animations

ui/compositor/compositor.cc

Index: ui/compositor/compositor.cc
diff --git a/ui/compositor/compositor.cc b/ui/compositor/compositor.cc
index dafe34d40683de9cd4fa7a999ea11e5e405ee883..d46b0c0aacf3843effa0dfea2e5b5a4a9f751ae1 100644
--- a/ui/compositor/compositor.cc
+++ b/ui/compositor/compositor.cc
@@ -83,6 +83,7 @@ Compositor::Compositor(const cc::FrameSinkId& frame_sink_id,
 #if defined(USE_AURA)
       window_(nullptr),
 #endif
+      submitted_frame_number_(0),
       widget_valid_(false),
       compositor_frame_sink_requested_(false),
       frame_sink_id_(frame_sink_id),
@@ -524,6 +525,7 @@ void Compositor::DidReceiveCompositorFrameAck() {
 }
 
 void Compositor::DidSubmitCompositorFrame() {
+  ++submitted_frame_number_;

[reveman, 2017/01/21 15:27:39]

This doesn't mean the frame was displayed. If we submit a bad frame (e.g. one
with lots of overdraw) we might still miss vsync and jank. Should these stats be
hooked up to swap acks instead?

[danakj, 2017/01/23 15:52:05]

Depends if we wanna measure the production of frames from the UI compositor or
the whole stack beyond it.

[varkha, 2017/01/24 00:18:57]

Looking at how WaitForSwap() is implemented I think wiring it to
DidReceiveCompositorFrameAck is the right thing to do if we want to measure what
a user actually sees ("whole stack").

   base::TimeTicks start_time = base::TimeTicks::Now();
   for (auto& observer : observer_list_)
     observer.OnCompositingStarted(this, start_time);