UMA metrics for use count of wheel and touch scrolls.

cc/trees/layer_tree_host_common.cc

Index: cc/trees/layer_tree_host_common.cc
diff --git a/cc/trees/layer_tree_host_common.cc b/cc/trees/layer_tree_host_common.cc
index 7f096be5b62583fcfef74a1839eb4abd66d0a576..132bc7a7c64553b3338dbaad582fd9ab581fa39b 100644
--- a/cc/trees/layer_tree_host_common.cc
+++ b/cc/trees/layer_tree_host_common.cc
@@ -180,8 +180,10 @@ bool LayerTreeHostCommon::ScrollbarsUpdateInfo::operator==(
 }
 
 ScrollAndScaleSet::ScrollAndScaleSet()
-    : page_scale_delta(1.f), top_controls_delta(0.f) {
-}
+    : page_scale_delta(1.f),
+      top_controls_delta(0.f),
+      has_scrolled_by_wheel(false),
+      has_scrolled_by_touch(false) {}
 
 ScrollAndScaleSet::~ScrollAndScaleSet() {}