Use element id's for animations

cc/layers/layer_impl.cc

Index: cc/layers/layer_impl.cc
diff --git a/cc/layers/layer_impl.cc b/cc/layers/layer_impl.cc
index c0badc3bd70ab98621bc2eec3dbb1ba0c42fdaef..65d9ce98b770948048ebec21f119ad3713c50d37 100644
--- a/cc/layers/layer_impl.cc
+++ b/cc/layers/layer_impl.cc
@@ -949,16 +949,25 @@ bool LayerImpl::HasPotentiallyRunningOpacityAnimation() const {
   return layer_tree_impl_->HasPotentiallyRunningOpacityAnimation(this);
 }
 
-void LayerImpl::SetElementId(uint64_t element_id) {
+void LayerImpl::SetElementId(ElementId element_id) {
   if (element_id == element_id_)
     return;
 
   TRACE_EVENT1(TRACE_DISABLED_BY_DEFAULT("compositor-worker"),
-               "LayerImpl::SetElementId", "id", element_id);
+               "LayerImpl::SetElementId", "element",
+               element_id.AsValue().release());
 
   layer_tree_impl_->RemoveFromElementMap(this);
   element_id_ = element_id;
   layer_tree_impl_->AddToElementMap(this);
+
+  PropertyTrees* property_trees = layer_tree_impl()->property_trees();
+  if (property_trees->IsInIdToIndexMap(PropertyTrees::TreeType::SCROLL, id())) {
+    ScrollNode* node = property_trees->scroll_tree.Node(
+        property_trees->scroll_id_to_index_map[id()]);
+    node->data.element_id = element_id_;
+  }

[ajuma, 2016/06/01 23:53:42]

The property trees pushed from the main thread will already have the new element
id, so I don't think we need to update property trees here.

[Ian Vollick, 2016/06/02 19:03:11]

You're right. The problem was that I'd called SetElementIdsForTesting after
building the property trees in layer_tree_host_impl_unittest.cc and this was
certainly the wrong fix. I've since updated the ordering and removed this code.

+
   SetNeedsPushProperties();
 }
 
@@ -1149,10 +1158,11 @@ void LayerImpl::AsValueInto(base::trace_event::TracedValue* state) const {
   state->SetInteger("gpu_memory_usage",
                     base::saturated_cast<int>(GPUMemoryUsageInBytes()));
 
-  if (mutable_properties_ != MutableProperty::kNone) {
-    state->SetInteger("element_id", base::saturated_cast<int>(element_id_));
+  if (element_id_)
+    element_id_.AddToTracedValue(state);
+
+  if (mutable_properties_ != MutableProperty::kNone)
     state->SetInteger("mutable_properties", mutable_properties_);
-  }
 
   MathUtil::AddToTracedValue("scroll_offset", CurrentScrollOffset(), state);