Introduce AXObjectCacheBase in core/ and remove WebNode dependency

third_party/WebKit/Source/core/dom/AXObjectCacheBase.h

Index: third_party/WebKit/Source/core/dom/AXObjectCacheBase.h
diff --git a/third_party/WebKit/Source/core/dom/AXObjectCacheBase.h b/third_party/WebKit/Source/core/dom/AXObjectCacheBase.h
new file mode 100644
index 0000000000000000000000000000000000000000..8992dfb4acf4c864b0b46803b7a2d0a7f4021dbc
--- /dev/null
+++ b/third_party/WebKit/Source/core/dom/AXObjectCacheBase.h
@@ -0,0 +1,39 @@
+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef AXObjectCacheBase_h
+#define AXObjectCacheBase_h
+
+#include "core/CoreExport.h"
+#include "core/dom/AXObjectCache.h"
+
+namespace blink {
+
+class Node;
+class AXObjectImpl;
+
+// AXObjectCacheBase is a temporary class that sits between AXObjectCache and
+// AXObjectImpl and contains methods required by web/ that we don't want to be
+// available in the public API (AXObjectCache).
+// TODO(dmazzoni): Once all dependencies in web/ use this class instead of
+// AXObjectCacheImpl, refactor usages to use AXObjectCache instead (introducing
+// new public API methods or similar) and remove this class.
+class CORE_EXPORT AXObjectCacheBase : public AXObjectCache {
+  WTF_MAKE_NONCOPYABLE(AXObjectCacheBase);
+
+ public:
+  virtual ~AXObjectCacheBase();
+
+  virtual AXObjectImpl* Get(Node*) = 0;
+
+ protected:
+  AXObjectCacheBase();
+};
+
+// This is the only subclass of AXObjectCache.
+DEFINE_TYPE_CASTS(AXObjectCacheBase, AXObjectCache, cache, true, true);
+
+}  // namespace blink
+
+#endif