Introduce few const getters for dom classes

third_party/WebKit/Source/core/dom/Node.cpp

Index: third_party/WebKit/Source/core/dom/Node.cpp
diff --git a/third_party/WebKit/Source/core/dom/Node.cpp b/third_party/WebKit/Source/core/dom/Node.cpp
index 78ab5e3ad08519f8cf1b09af1f4f41dab355e0bf..2547443457442477a9445ea392d598c18d2af1c8 100644
--- a/third_party/WebKit/Source/core/dom/Node.cpp
+++ b/third_party/WebKit/Source/core/dom/Node.cpp
@@ -339,6 +339,11 @@ NodeRareData* Node::rareData() const
     return static_cast<NodeRareData*>(m_data.m_rareData);
 }
 
+NodeRareData* Node::maybeRareData() const
+{
+    return hasRareData() ? rareData() : nullptr;
+}
+
 NodeRareData& Node::ensureRareData()
 {
     if (hasRareData())
@@ -1892,14 +1897,14 @@ void Node::removeAllEventListenersRecursively()
     }
 }
 
-using EventTargetDataMap = HeapHashMap<WeakMember<Node>, Member<EventTargetData>>;
+using EventTargetDataMap = HeapHashMap<WeakMember<const Node>, Member<EventTargetData>>;
 static EventTargetDataMap& eventTargetDataMap()
 {
     DEFINE_STATIC_LOCAL(EventTargetDataMap, map, (new EventTargetDataMap));
     return map;
 }
 
-EventTargetData* Node::eventTargetData()
+EventTargetData* Node::eventTargetData() const
 {
     return hasEventTargetData() ? eventTargetDataMap().get(this) : nullptr;
 }