Plumb PinchVirtualViewport layers into CC.

cc/trees/layer_tree_host.cc

Index: cc/trees/layer_tree_host.cc
diff --git a/cc/trees/layer_tree_host.cc b/cc/trees/layer_tree_host.cc
index 611d6aee0a1df4c242c2ece7b9c88a8bc557ea5c..dea57577216875db94ac4e155cb3def7d83c48c7 100644
--- a/cc/trees/layer_tree_host.cc
+++ b/cc/trees/layer_tree_host.cc
@@ -330,6 +330,19 @@ void LayerTreeHost::FinishCommitOnImplThread(LayerTreeHostImpl* host_impl) {
 
   sync_tree->FindRootScrollLayer();
 
+  // TODO(wjmaclean) For now, not all LTH clients will register viewports, so
+  // only set them when available..
+  if (page_scale_layer_) {
+    DCHECK(inner_viewport_scroll_layer_);
+    sync_tree->SetViewportLayersFromIds(
+        page_scale_layer_->id(),
+        inner_viewport_scroll_layer_->id(),
+        outer_viewport_scroll_layer_ ? outer_viewport_scroll_layer_->id()
+                                     : Layer::INVALID_ID);
+  } else {
+    sync_tree->ClearViewportLayers();
+  }
+
   float page_scale_delta, sent_page_scale_delta;
   if (settings_.impl_side_painting) {
     // Update the delta from the active tree, which may have
@@ -758,6 +771,9 @@ bool LayerTreeHost::UpdateLayers(Layer* root_layer,
     UpdateHudLayer();
 
     Layer* root_scroll = FindFirstScrollableLayer(root_layer);
+    Layer* page_scale_layer = page_scale_layer_;
+    if (!page_scale_layer && root_scroll)
+      page_scale_layer = root_scroll->parent();
 
     if (hud_layer_) {
       hud_layer_->PrepareForCalculateDrawProperties(
@@ -771,7 +787,7 @@ bool LayerTreeHost::UpdateLayers(Layer* root_layer,
         gfx::Transform(),
         device_scale_factor_,
         page_scale_factor_,
-        root_scroll ? root_scroll->parent() : NULL,
+        page_scale_layer,
         GetRendererCapabilities().max_texture_size,
         settings_.can_use_lcd_text,
         settings_.layer_transforms_should_scale_layer_contents,
@@ -1188,4 +1204,13 @@ void LayerTreeHost::RecreateUIResources() {
   }
 }
 
+void LayerTreeHost::RegisterViewportLayers(
+    scoped_refptr<Layer> page_scale_layer,
+    scoped_refptr<Layer> inner_viewport_scroll_layer,
+    scoped_refptr<Layer> outer_viewport_scroll_layer) {
+  page_scale_layer_ = page_scale_layer;
+  inner_viewport_scroll_layer_ = inner_viewport_scroll_layer;
+  outer_viewport_scroll_layer_ = outer_viewport_scroll_layer;
+}
+
 }  // namespace cc