Adding tracing to measure synthetic smooth scrolling correctness

cc/scrollbar_animation_controller.cc

Index: cc/scrollbar_animation_controller.cc
diff --git a/cc/scrollbar_animation_controller.cc b/cc/scrollbar_animation_controller.cc
index 4d75877d2efcb9f31cea5d2f3dac5911bf98a278..1d9151b11e1556231341179f18fe919feb4a0c3f 100644
--- a/cc/scrollbar_animation_controller.cc
+++ b/cc/scrollbar_animation_controller.cc
@@ -4,6 +4,7 @@
 
 #include "cc/scrollbar_animation_controller.h"
 
+#include "base/debug/trace_event.h"
 #include "base/time.h"
 #include "build/build_config.h"
 #include "cc/scrollbar_layer_impl.h"
@@ -80,6 +81,12 @@ void ScrollbarAnimationController::updateScrollOffsetAtTime(LayerImpl* scrollLay
     m_totalSize = getScrollLayerBounds(scrollLayer);
     m_maximum = scrollLayer->maxScrollOffset();
 
+    // Get the m_currentOffset.y() value for a sanity-check on scrolling
+    // benchmark metrics. Specifically, we want to make sure
+    // BasicMouseWheelSmoothScrollGesture has proper scroll curves.
+    TRACE_COUNTER_ID1("gpu", "scroll_offset_y", this, m_currentOffset.y());

[nduca, 2013/01/04 22:42:13]

we should be passing a layerTreeHostImpl pointer here.

+
+
     if (m_horizontalScrollbarLayer) {
         m_horizontalScrollbarLayer->setCurrentPos(m_currentOffset.x());
         m_horizontalScrollbarLayer->setTotalSize(m_totalSize.width());