GPU benchmarks should track the frequency of impl-thread vs. main-thread scrolls

cc/CCLayerTreeHostImpl.cpp

Index: cc/CCLayerTreeHostImpl.cpp
diff --git a/cc/CCLayerTreeHostImpl.cpp b/cc/CCLayerTreeHostImpl.cpp
index 479348230892e799dbfa1596f84d39483b501013..606ed38a0e819c25b126f336a721d776c1e0d8fe 100644
--- a/cc/CCLayerTreeHostImpl.cpp
+++ b/cc/CCLayerTreeHostImpl.cpp
@@ -937,6 +937,7 @@ CCInputHandlerClient::ScrollStatus CCLayerTreeHostImpl::scrollBegin(const IntPoi
         // so that the scrolling contents exactly follow the user's finger. In contrast, wheel
         // events are already in local layer coordinates so we can just apply them directly.
         m_scrollDeltaIsInScreenSpace = (type == Gesture);
+        m_didImplThreadScroll = true;
         return ScrollStarted;
     }
     return ScrollIgnored;
@@ -1034,6 +1035,7 @@ void CCLayerTreeHostImpl::clearCurrentlyScrollingLayer()
 {
     m_currentlyScrollingLayerImpl = 0;
     m_scrollingLayerIdFromPreviousTree = -1;
+    m_didImplThreadScroll = false;

[enne (OOO), 2012/09/28 18:54:29]

This seems a little weird to me.  If a scroll gesture begins and ends before you
call rendering stats, then this value will be false.  Would it make sense to
instead keep track of some count and report it or the delta since the last time
rendering stats was called?

[tdanderson, 2012/10/01 19:38:12]

Thanks for the feedback. Instead of using a boolean, now I'm tracking the
frequency of each scroll type with two counters.

 }
 
 void CCLayerTreeHostImpl::scrollEnd()
@@ -1288,6 +1290,7 @@ void CCLayerTreeHostImpl::renderingStats(CCRenderingStats* stats) const
 {
     stats->numFramesSentToScreen = fpsCounter()->currentFrameNumber();
     stats->droppedFrameCount = fpsCounter()->droppedFrameCount();
+    stats->didImplThreadScroll = m_didImplThreadScroll;
 }
 
 void CCLayerTreeHostImpl::animateScrollbars(double monotonicTime)