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

cc/layer_tree_impl.cc

Index: cc/layer_tree_impl.cc
diff --git a/cc/layer_tree_impl.cc b/cc/layer_tree_impl.cc
index d434bb0e6a2a4f78f1706fa3740720224f8bc1d0..60e85decb6cf191cb9c234784d61e7b7f177b9b9 100644
--- a/cc/layer_tree_impl.cc
+++ b/cc/layer_tree_impl.cc
@@ -6,6 +6,7 @@
 
 #include "cc/layer_tree_host_common.h"
 #include "cc/layer_tree_host_impl.h"
+#include "cc/pinch_zoom_scrollbars_manager.h"
 
 namespace cc {
 
@@ -13,9 +14,13 @@ LayerTreeImpl::LayerTreeImpl(LayerTreeHostImpl* layer_tree_host_impl)
     : layer_tree_host_impl_(layer_tree_host_impl)
     , source_frame_number_(-1)
     , hud_layer_(0)
+    , pinch_zoom_scrollbar_vertical_(0)
+    , pinch_zoom_scrollbar_horizontal_(0)
     , root_scroll_layer_(0)
     , currently_scrolling_layer_(0)
     , scrolling_layer_id_from_previous_tree_(0) {
+  if (settings().pageScalePinchZoomEnabled)
+    pinch_zoom_scrollbars_ = PinchZoomScrollbarsManager::create();
 }
 
 LayerTreeImpl::~LayerTreeImpl() {
@@ -54,6 +59,20 @@ void LayerTreeImpl::SetRootLayer(scoped_ptr<LayerImpl> layer) {
   layer_tree_host_impl_->OnCanDrawStateChangedForTree(this);
 }
 
+void LayerTreeImpl::set_pinch_zoom_scrollbar_vertical(ScrollbarLayerImpl* layer_impl)
+{
+  pinch_zoom_scrollbar_vertical_ = layer_impl;
+  if (pinch_zoom_scrollbars_)
+    pinch_zoom_scrollbars_->setScrollbarVertical(layer_impl);
+}
+
+void LayerTreeImpl::set_pinch_zoom_scrollbar_horizontal(ScrollbarLayerImpl* layer_impl)
+{
+  pinch_zoom_scrollbar_horizontal_ = layer_impl;
+  if (pinch_zoom_scrollbars_)
+    pinch_zoom_scrollbars_->setScrollbarHorizontal(layer_impl);
+}
+
 scoped_ptr<LayerImpl> LayerTreeImpl::DetachLayerTree() {
   // Clear all data structures that have direct references to the layer tree.
   scrolling_layer_id_from_previous_tree_ =