Move nonscrollable axis gloweffect suppression to renderer.

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 685cfb99122f393eec5b610e90c35c8c51ed546d..eced362eacae6b604634276c36354246437b80c1 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -2313,6 +2313,20 @@ bool LayerTreeHostImpl::ScrollBy(const gfx::Point& viewport_point,
         unused_root_delta.set_x(0.0f);
       if (std::abs(unused_root_delta.y()) < kEpsilon)
         unused_root_delta.set_y(0.0f);
+      // Disable overscroll on axes which is impossible to scroll.
+      if (settings_.report_overscroll_only_for_scrollable_axes) {
+        gfx::SizeF ceiled_viewport_size =

[jdduke (slow), 2014/04/10 14:16:02]

You shouldn't need to check both viewport size and the max scroll offset,
something like this should be sufficient:

if (active_tree_->TotalMaxScrollOffset().x() <= kEpsilon)
  unused_root_delta.set_x(0.0f):
if (active_tree_->TotalMaxScrollOffset().y() <= kEpsilon)
  unused_root_delta.set_y(0.0f):

+            gfx::ToCeiledSize(active_tree_->ScrollableViewportSize());
+        gfx::SizeF root_layer_size = active_tree_->ScrollableSize();
+        if (!(ceiled_viewport_size.width() < root_layer_size.width())) {
+          if (std::abs(InnerViewportScrollLayer()->MaxScrollOffset().x()) <= 0)

[aelias_OOO_until_Jul13, 2014/04/10 16:28:37]

Please also check OuterViewportScrollLayer as I mentioned earlier.  For context,
this is for when this approach launches in the future:
https://docs.google.com/a/chromium.org/document/d/1KewSqexq4Pd99RUFB-yVoUIJoc...

+            unused_root_delta.set_x(0.0f);
+        }
+        if (!(ceiled_viewport_size.height() < root_layer_size.height())) {
+          if (std::abs(InnerViewportScrollLayer()->MaxScrollOffset().y()) <= 0)
+            unused_root_delta.set_y(0.0f);
+        }
+      }
     }
 
     // If the layer wasn't able to move, try the next one in the hierarchy.