Add Maplike<> utility mixin class for implementing maplike interfaces

Source/core/dom/Maplike.h

Index: Source/core/dom/Maplike.h
diff --git a/Source/core/dom/Maplike.h b/Source/core/dom/Maplike.h
new file mode 100644
index 0000000000000000000000000000000000000000..8d001413df1e6dd90af5108fcc3fd97272873856
--- /dev/null
+++ b/Source/core/dom/Maplike.h
@@ -0,0 +1,37 @@
+// Copyright 2015 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 Maplike_h
+#define Maplike_h
+
+#include "bindings/core/v8/ScriptValue.h"
+#include "bindings/core/v8/ToV8.h"
+#include "core/dom/Iterable.h"
+
+namespace blink {
+
+template <typename KeyType, typename ValueType>
+class Maplike : public PairIterable<KeyType, ValueType> {
+public:
+    bool hasForBinding(ScriptState* scriptState, const KeyType& key, ExceptionState& exceptionState)
+    {
+        ValueType value;
+        return getMapEntry(scriptState, key, value, exceptionState);
+    }
+
+    ScriptValue getForBinding(ScriptState* scriptState, const KeyType& key, ExceptionState& exceptionState)
+    {
+        ValueType value;
+        if (getMapEntry(scriptState, key, value, exceptionState))
+            return ScriptValue(scriptState, toV8(value, scriptState->context()->Global(), scriptState->isolate()));
+        return ScriptValue(scriptState, v8::Undefined(scriptState->isolate()));
+    }
+
+private:
+    virtual bool getMapEntry(ScriptState*, const KeyType&, ValueType&, ExceptionState&) = 0;
+};
+
+} // namespace blink
+
+#endif // Maplike_h