oilpan: Trace Node::GetEventTargetData()

The target object is already traced in Oilpan from a static persistent map,
but this CL adds a trace to make TraceWrappers() a subset of
Trace() for unification.


Bug: 841830
Change-Id: I3bec0361aa34ac7a0dc82fcb0cf3d823ea58057a
Reviewed-on: https://chromium-review.googlesource.com/1055013
Commit-Queue: Hitoshi Yoshida <peria@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#558197}

third_party/blink/renderer/core/dom/node.cc

@@ -2765,13 +2765,12 @@ void Node::Trace(blink::Visitor* visitor) {
   visitor->Trace(parent_or_shadow_host_node_);
   visitor->Trace(previous_);
   visitor->Trace(next_);
-  // rareData() and m_data.m_layoutObject share their storage. We have to trace
-  // only one of them.
+  // rareData() and data_.node_layout_data_ share their storage. We have to
+  // trace only one of them.
   if (HasRareData())
     visitor->Trace(RareData());
-
+  visitor->Trace(GetEventTargetData());
   visitor->Trace(tree_scope_);
-  // EventTargetData is traced through EventTargetDataMap.
   EventTarget::Trace(visitor);
 }