Hide scrollbars when their dimensions are not scrollable.

cc/layers/layer_impl.h

Index: cc/layers/layer_impl.h
diff --git a/cc/layers/layer_impl.h b/cc/layers/layer_impl.h
index 3465e0e085e5aa98d45d80d56cd2d6ef8008a2fb..76427a1e53bb9f8a10bac234d51b2324aee6f42d 100644
--- a/cc/layers/layer_impl.h
+++ b/cc/layers/layer_impl.h
@@ -19,6 +19,7 @@
 #include "cc/base/region.h"
 #include "cc/base/scoped_ptr_vector.h"
 #include "cc/input/input_handler.h"
+#include "cc/input/scrollbar.h"
 #include "cc/layers/draw_properties.h"
 #include "cc/layers/layer_lists.h"
 #include "cc/layers/layer_position_constraint.h"
@@ -419,6 +420,8 @@ class CC_EXPORT LayerImpl : public LayerAnimationValueObserver,
   }
   bool user_scrollable_vertical() const { return user_scrollable_vertical_; }
 
+  bool user_scrollable(ScrollbarOrientation orientation) const;
+
   void ApplySentScrollDeltasFromAbortedCommit();
   void ApplyScrollDeltasSinceBeginMainFrame();