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

cc/scrollbar_layer_impl.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_impl.h"
 
+#include "cc/layer.h"
 #include "cc/layer_tree_impl.h"
 #include "cc/layer_tree_settings.h"
 #include "cc/quad_sink.h"
 #include "cc/scrollbar_animation_controller.h"
 #include "cc/solid_color_draw_quad.h"
 #include "cc/texture_draw_quad.h"
 #include "ui/gfx/rect_conversions.h"
 
 using WebKit::WebRect;
 using WebKit::WebScrollbar;
@@ skipping 16 matching lines @@
     : ScrollbarLayerImplBase(tree_impl, id),
       scrollbar_(this),
       back_track_resource_id_(0),
       fore_track_resource_id_(0),
       thumb_resource_id_(0),
       geometry_(geometry.Pass()),
       current_pos_(0),
       total_size_(0),
       maximum_(0),
       vertical_adjust_(0.f),
-      scroll_layer_id_(-1),
+      scroll_layer_id_(Layer::INVALID_ID),
       scrollbar_overlay_style_(WebScrollbar::ScrollbarOverlayStyleDefault),
       orientation_(WebScrollbar::Horizontal),
       control_size_(WebScrollbar::RegularScrollbar),
       pressed_part_(WebScrollbar::NoPart),
       hovered_part_(WebScrollbar::NoPart),
       is_scrollable_area_active_(false),
       is_scroll_view_scrollbar_(false),
       enabled_(false),
       is_custom_scrollbar_(false),
       is_overlay_scrollbar_(false) {}
@@ skipping 278 matching lines @@
 
 bool ScrollbarLayerImpl::Scrollbar::isCustomScrollbar() const {
   return owner_->is_custom_scrollbar_;
 }
 
 const char* ScrollbarLayerImpl::LayerTypeAsString() const {
   return "ScrollbarLayer";
 }
 
 }  // namespace cc