Hide scrollbars when their dimensions are not scrollable.

cc/animation/scrollbar_animation_controller_linear_fade.cc

Index: cc/animation/scrollbar_animation_controller_linear_fade.cc
diff --git a/cc/animation/scrollbar_animation_controller_linear_fade.cc b/cc/animation/scrollbar_animation_controller_linear_fade.cc
index 90437b3835b322c09649fe35d024d603d05bcc0b..f65fd727ac4fe50f9c8666ac3489a8426eb59b6a 100644
--- a/cc/animation/scrollbar_animation_controller_linear_fade.cc
+++ b/cc/animation/scrollbar_animation_controller_linear_fade.cc
@@ -62,8 +62,9 @@ void ScrollbarAnimationControllerLinearFade::ApplyOpacityToScrollbars(
        it != scrollbars->end();
        ++it) {
     ScrollbarLayerImplBase* scrollbar = *it;
+
     if (scrollbar->is_overlay_scrollbar())
-      scrollbar->SetOpacity(opacity);
+      scrollbar->SetOpacity(scrollbar->can_scroll_orientation() ? opacity : 0);
   }
 }