[Android]Optimization of scrollbar animation.

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 231 matching lines @@
   return ScrollbarLayerRectToContentRect(thumb_rect);
 }
 
 void ScrollbarLayerImplBase::ScrollbarParametersDidChange() {
   if (!clip_layer_ || !scroll_layer_)
     return;
 
   scroll_layer_->SetScrollbarPosition(this, clip_layer_);
 }
 
+bool ScrollbarLayerImplBase::ScrollbarNeedsUpdate(
+    float vertical_adjust,
+    float current_pos,
+    int maximum,
+    float visible_to_total_length_ratio) {
+  if ((vertical_adjust != vertical_adjust_) || (current_pos != current_pos_) ||
+      (maximum != maximum_) ||
+      (visible_to_total_length_ratio != visible_to_total_length_ratio_))
+    return true;
+  return false;
+}
+
 }  // namespace cc