Avoid unnecessary gloweffect calls

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index 958419eb306af5bcd1bc1b8a0b022095b9941ee5..e00dc516f8ce9c3c5d1841e7472eb8ec1223613a 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -2314,6 +2314,14 @@ bool LayerTreeHostImpl::ScrollBy(const gfx::Point& viewport_point,
     accumulated_root_overscroll_.set_y(0);
 
   accumulated_root_overscroll_ += unused_root_delta;
+
+  // Scrolling along an axis resets unused root delta which unnecessarily calls
+  // glow effect

[danakj, 2014/03/20 17:01:30]

nit: missing period

+  if (did_scroll_x)
+    unused_root_delta.set_y(0);
+  if (did_scroll_y)
+    unused_root_delta.set_x(0);
+
   bool did_overscroll = !gfx::ToRoundedVector2d(unused_root_delta).IsZero();

[aelias_OOO_until_Jul13, 2014/03/21 00:16:11]

And this can be simplified to:

bool did_overscroll = !unused_root_delta.IsZero();

   if (did_overscroll && input_handler_client_) {
     DidOverscrollParams params;