Introduce MIDIInputMap and MIDIOutputMap.

Source/modules/webmidi/MIDIInputMap.cpp

+// Copyright 2014 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.
+
+#include "config.h"
+#include "modules/webmidi/MIDIInputMap.h"
+
+#include "bindings/core/v8/ScriptState.h"
+#include "bindings/modules/v8/V8MIDIInput.h"
+
+namespace blink {
+
+ScriptValue MIDIInputMap::getForBinding(ScriptState* scriptState, const String& id)
+{
+    MIDIInput* result = get(id);
+    if (result)
+        return ScriptValue(scriptState, toV8(result, scriptState->context()->Global(), scriptState->isolate()));
+    return ScriptValue(scriptState, v8::Undefined(scriptState->isolate()));
+}
+
+} // namespace blink
+