Hide scrollbars when their dimensions are not scrollable.

cc/layers/scrollbar_layer_impl_base.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/layers/scrollbar_layer_impl_base.h"
 
 #include <algorithm>
 #include "cc/trees/layer_tree_impl.h"
 #include "ui/gfx/rect_conversions.h"
 
@@ skipping 104 matching lines @@
 }
 
 bool ScrollbarLayerImplBase::SetMaximum(int maximum) {
   if (maximum_ == maximum)
     return false;
   maximum_ = maximum;
   NoteLayerPropertyChanged();
   return true;
 }
 
+bool ScrollbarLayerImplBase::CanScrollOrientation() const {
+  if (!scroll_layer_)
+    return false;
+  return scroll_layer_->user_scrollable(orientation()) && (0 < maximum());
+}
+
 bool ScrollbarLayerImplBase::SetVerticalAdjust(float vertical_adjust) {
   if (vertical_adjust_ == vertical_adjust)
     return false;
   vertical_adjust_ = vertical_adjust;
   NoteLayerPropertyChanged();
   return true;
 }
 
 bool ScrollbarLayerImplBase::SetVisibleToTotalLengthRatio(float ratio) {
   if (!IsThumbResizable())
@@ skipping 114 matching lines @@
 }
 
 void ScrollbarLayerImplBase::ScrollbarParametersDidChange(bool on_resize) {
   if (!clip_layer_ || !scroll_layer_)
     return;
 
   scroll_layer_->SetScrollbarPosition(this, clip_layer_, on_resize);
 }
 
 }  // namespace cc