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..a4b995bcb0d45a71d7f4dd52469ec13d0b2c8827 100644
--- a/cc/animation/scrollbar_animation_controller_linear_fade.cc
+++ b/cc/animation/scrollbar_animation_controller_linear_fade.cc
@@ -62,8 +62,11 @@ void ScrollbarAnimationControllerLinearFade::ApplyOpacityToScrollbars(
        it != scrollbars->end();
        ++it) {
     ScrollbarLayerImplBase* scrollbar = *it;
-    if (scrollbar->is_overlay_scrollbar())
-      scrollbar->SetOpacity(opacity);
+    if (scrollbar->is_overlay_scrollbar()) {
+      bool visible = scroll_layer_->user_scrollable(scrollbar->orientation()) &&

[aelias_OOO_until_Jul13, 2014/10/13 18:30:03]

How about moving this logic to a method on ScrollbarLayerImplBase, called
scrollable()?

+                     scrollbar->maximum() > 0;
+      scrollbar->SetOpacity(visible ? opacity : 0);
+    }
   }
 }