Update cc effect node documentation.

cc/trees/effect_node.h

Index: cc/trees/effect_node.h
diff --git a/cc/trees/effect_node.h b/cc/trees/effect_node.h
index 81ee42f1071f1964b371bee47d4f61cf9e043719..2bfb0be4570e952e98af568585e1a2b50a06e2dc 100644
--- a/cc/trees/effect_node.h
+++ b/cc/trees/effect_node.h
@@ -51,20 +51,35 @@ struct CC_EXPORT EffectNode {
   // TODO(jaydasika) : Delete this after implementation of
   // SetHideLayerAndSubtree is cleaned up. (crbug.com/595843)
   bool subtree_hidden;
+  // Whether this node has a potentially running (i.e., irrespective
+  // of exact timeline) filter animation.
   bool has_potential_filter_animation;

[pdr., 2017/05/18 23:52:47]

Is it just for this node, or this node or any ancestor node?

[wkorman, 2017/05/19 00:37:03]

Just this node.

+  // Whether this node has a potentially running (i.e., irrespective
+  // of exact timeline) opacity animation.
   bool has_potential_opacity_animation;
+  // Whether this node has a currently running filter animation.
   bool is_currently_animating_filter;
+  // Whether this node has a currently running opacity animation.
   bool is_currently_animating_opacity;
-  // We need to track changes to effects on the compositor to compute damage
-  // rect.
+  // Whether this node's effect has been changed since last

[pdr., 2017/05/18 23:52:47]

Nit: since [the] last frame.

[wkorman, 2017/05/19 00:37:03]

Done.

+  // frame. Needed in order to compute damage rect.
   bool effect_changed;
   bool subtree_has_copy_request;
+  // The transform node index of the transform to apply to this effect
+  // node's content when rendering to a surface.
   int transform_id;
+  // The clip node index of the clip to apply to this effect node's
+  // content when rendering to a surface.
   int clip_id;
 
   // This is the id of the ancestor effect node that induces a
   // RenderSurfaceImpl.
   int target_id;
+  // The layer id of the mask layer, if any, to apply to this effect
+  // node's content when rendering to a surface.
+  // TODO(wkorman): It appears the only reads of this value are to

[wkorman, 2017/05/18 23:57:03]

I found the one reference of impact -- RenderSurfaceImpl::MaskLayer uses this to
look up the layer by id. I must have missed in my previous searching. Will
remove this TODO.

+  // determine whether the node has a mask for occlusion tracking
+  // purposes. Perhaps it can just be a bool?
   int mask_layer_id;
   int closest_ancestor_with_copy_request_id;