Introduce AXObjectCacheBase in core/ and remove WebNode dependency

third_party/WebKit/Source/web/WebNode.cpp

Index: third_party/WebKit/Source/web/WebNode.cpp
diff --git a/third_party/WebKit/Source/web/WebNode.cpp b/third_party/WebKit/Source/web/WebNode.cpp
index 12105550b775712c471db8d80a94121ac84486e8..7b9846c88e07456b7d24f01f17564d257483ff5d 100644
--- a/third_party/WebKit/Source/web/WebNode.cpp
+++ b/third_party/WebKit/Source/web/WebNode.cpp
@@ -31,6 +31,7 @@
 #include "public/web/WebNode.h"
 
 #include "bindings/core/v8/ExceptionState.h"
+#include "core/dom/AXObjectCacheBase.h"
 #include "core/dom/Document.h"
 #include "core/dom/Element.h"
 #include "core/dom/Node.h"
@@ -198,7 +199,7 @@ WebPluginContainer* WebNode::PluginContainer() const {
 WebAXObject WebNode::AccessibilityObject() {
   WebDocument web_document = GetDocument();
   const Document* doc = GetDocument().ConstUnwrap<Document>();
-  AXObjectCacheImpl* cache = ToAXObjectCacheImpl(doc->ExistingAXObjectCache());
+  AXObjectCacheBase* cache = ToAXObjectCacheBase(doc->ExistingAXObjectCache());
   Node* node = Unwrap<Node>();
   return cache ? WebAXObject(cache->Get(node)) : WebAXObject();
 }