cc : Use effect node data to determine which opacity wins at commit.

cc/trees/layer_tree_impl.cc

Index: cc/trees/layer_tree_impl.cc
diff --git a/cc/trees/layer_tree_impl.cc b/cc/trees/layer_tree_impl.cc
index 74603d51fbc0f1016e5cc45cfd7ffa8a6b09b4a4..5cc14543da1a5605580dd9d3da8c40ff6e73eda5 100644
--- a/cc/trees/layer_tree_impl.cc
+++ b/cc/trees/layer_tree_impl.cc
@@ -484,6 +484,10 @@ void LayerTreeImpl::RemoveFromElementMap(LayerImpl* layer) {
     element_layers_map_.erase(layer->element_id());
 }
 
+void LayerTreeImpl::AddToOpacityAnimationsMap(int id, float opacity) {
+  opacity_animations_map_[id] = opacity;
+}
+
 LayerTreeImpl::ElementLayers LayerTreeImpl::GetMutableLayers(
     uint64_t element_id) {
   auto iter = element_layers_map_.find(element_id);
@@ -562,6 +566,19 @@ void LayerTreeImpl::UpdatePropertyTreeScrollingAndAnimationFromMainThread() {
   // frame to a newly-committed property tree.
   if (!root_layer())
     return;
+  for (auto& layer_id_to_opacity : opacity_animations_map_) {
+    if (LayerImpl* layer = LayerById(layer_id_to_opacity.first)) {

[ajuma, 2016/05/11 00:10:59]

We'll need a map from layer ids to node ids (which will eventually become a map
from stable node ids to node ids) so that we don't need to find the owning layer
here, but that can be done in a separate CL.

[jaydasika, 2016/05/11 01:00:54]

Acknowledged.

+      EffectNode* node =
+          property_trees_.effect_tree.Node(layer->effect_tree_index());
+      if (node->owner_id != layer->id() ||
+          !node->data.is_currently_animating_opacity)
+        continue;
+      DCHECK_EQ(layer->opacity(), layer_id_to_opacity.second);
+      node->data.opacity = layer_id_to_opacity.second;
+      property_trees_.effect_tree.set_needs_update(true);
+    }
+  }
+  opacity_animations_map_.clear();

[ajuma, 2016/05/11 00:11:00]

What kind of test coverage do we have for this logic right now? Are there tests
that fail if we don't update the value in the property tree node, or if we don't
clear the map?

[jaydasika, 2016/05/11 01:00:54]

There is only one unit test hitting this path :
LayerTreeHostAnimationTestCheckerboardDoesntStartAnimations. I have added one
more.

   LayerTreeHostCommon::CallFunctionForEveryLayer(this, [](LayerImpl* layer) {
     layer->UpdatePropertyTreeForScrollingAndAnimationIfNeeded();
   });