Update cc effect node documentation.

cc/trees/property_tree_builder.cc

 // Copyright 2014 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/trees/property_tree_builder.h"
 
 #include <stddef.h>
 
 #include <map>
 #include <set>
@@ skipping 930 matching lines @@
     // surface.
     if (should_create_render_surface) {
       // In this case, we will create a transform node, so it's safe to use the
       // next available id from the transform tree as this effect node's
       // transform id.
       node->transform_id =
           data_from_ancestor.property_trees->transform_tree.next_available_id();
     }
     node->clip_id = data_from_ancestor.clip_tree_parent;
   } else {
-    // Root render surface acts the unbounded and untransformed to draw content
-    // into. Transform node created from root layer (includes device scale
-    // factor) and clip node created from root layer (include viewports) applies
-    // to root render surface's content, but not root render surface itself.
+    // The root render surface acts as the unbounded and untransformed
+    // surface into which content is drawn. The transform node created
+    // from the root layer (which includes device scale factor) and
+    // the clip node created from the root layer (which includes
+    // viewports) apply to the root render surface's content, but not
+    // to the root render surface itself.
     node->transform_id = TransformTree::kRootNodeId;
     node->clip_id = ClipTree::kViewportNodeId;
   }
 
   data_for_children->closest_ancestor_with_copy_request =
       node->closest_ancestor_with_copy_request_id;
   data_for_children->effect_tree_parent = node_id;
   layer->SetEffectTreeIndex(node_id);
   data_for_children->property_trees->effect_tree.SetOwningLayerIdForNode(
       effect_tree.back(), layer->id());
@@ skipping 413 matching lines @@
       root_layer, page_scale_layer, inner_viewport_scroll_layer,
       outer_viewport_scroll_layer, overscroll_elasticity_layer,
       elastic_overscroll, page_scale_factor, device_scale_factor, viewport,
       device_transform, property_trees, color);
   property_trees->effect_tree.CreateOrReuseRenderSurfaces(
       &render_surfaces, root_layer->layer_tree_impl());
   property_trees->ResetCachedData();
 }
 
 }  // namespace cc