Introduce MIDIInputMap and MIDIOutputMap.

Source/modules/webmidi/MIDIOutputMap.idl

Index: Source/modules/webmidi/MIDIOutputMap.idl
diff --git a/Source/modules/webmidi/MIDIOutputMap.idl b/Source/modules/webmidi/MIDIOutputMap.idl
new file mode 100644
index 0000000000000000000000000000000000000000..eec7a882b7bbb81bb0c62a10977b532777e11de2
--- /dev/null
+++ b/Source/modules/webmidi/MIDIOutputMap.idl
@@ -0,0 +1,22 @@
+// 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.
+
+// FIXME: Implement forEach.
+// callback ForEachCallback = void(DOMString id, MIDIOutput port);
+
+[
+    Iterable,
+    NoInterfaceObject,
+    GarbageCollected,
+] interface MIDIOutputMap {
+    readonly attribute unsigned long size;
+    Iterator keys();
+    Iterator entries();
+    Iterator values();
+    // This function returns undefined if |!this->has(id)|.
+    [ImplementedAs=getForBinding, CallWith=ScriptState] any get(DOMString id);
+    boolean has(DOMString key);
+    // FIXME: Implement forEach.
+    // void forEach (ForEachCallback callback);
+};