[android] Remove unused scroll delta in TopControls

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 c5b9566fc070a1d554a63823d31fd26135e972de..3b4f724104f6c8b2364b9e3e243cfb500a39bc25 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -2662,6 +2662,8 @@ bool LayerTreeHostImpl::ScrollBy(const gfx::Point& viewport_point,
             !layer_impl->user_scrollable_vertical())
           unused_root_delta.set_y(0.0f);
       }
+      if (consume_by_top_controls && unused_root_delta.y() > 0.0f)

[jdduke (slow), 2014/10/16 21:29:17]

Can you think of a solution that limits how much LTHI needs to know about the
TopControlsManager internals? For example, what if we avoid feeding the
TopControlsManager the |pending_delta| above if the root layer is at the max
limit of its scrollable area and the delta is positive? That could be folded
into the |ShouldTopControlsConsumeScroll| query.

[sujith, 2014/10/17 14:51:04]

Done.

+        top_controls_manager_->RemoveUnUsedScrollDelta(unused_root_delta.y());
     }
 
     // If the layer wasn't able to move, try the next one in the hierarchy.