Implement pinch-zoom scaling for main-frame scrollbars and pinch-zoom overlay scrollbars.

cc/scrollbar_layer.cc

 // Copyright 2012 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/scrollbar_layer.h"
 
 #include "base/basictypes.h"
 #include "base/debug/trace_event.h"
 #include "cc/caching_bitmap_content_layer_updater.h"
 #include "cc/layer_painter.h"
@@ skipping 111 matching lines @@
     scrollbar_layer->set_fore_track_resource_id(
         fore_track_->texture()->resourceId());
   } else {
     scrollbar_layer->set_fore_track_resource_id(0);
   }
 
   if (thumb_ && thumb_->texture()->haveBackingTexture())
     scrollbar_layer->set_thumb_resource_id(thumb_->texture()->resourceId());
   else
     scrollbar_layer->set_thumb_resource_id(0);
+
+  // Pinch zoom scrollbarLayerImpl does not get its scroll_layer_id_
+  // set in LayerImpl, so we need to push it here.
+  if (scroll_layer_id_ == Layer::PINCH_ZOOM_ROOT_SCROLL_LAYER_ID)
+    scrollbar_layer->set_scroll_layer_id(scroll_layer_id_);
 }
 
 ScrollbarLayer* ScrollbarLayer::ToScrollbarLayer() {
   return this;
 }
 
 class ScrollbarBackgroundPainter : public LayerPainter {
  public:
   static scoped_ptr<ScrollbarBackgroundPainter> Create(
       WebKit::WebScrollbar* scrollbar,
@@ skipping 281 matching lines @@
                thumb_.get(),
                origin_thumb_rect,
                queue,
                stats);
   }
 
   dirty_rect_ = gfx::RectF();
 }
 
 }  // namespace cc