Add Maplike<> utility mixin class for implementing maplike interfaces

Source/modules/webmidi/MIDIOutputMap.cpp

Index: Source/modules/webmidi/MIDIOutputMap.cpp
diff --git a/Source/modules/webmidi/MIDIOutputMap.cpp b/Source/modules/webmidi/MIDIOutputMap.cpp
index fb6c4ec154778c662d0a26e2773e23a1fd073626..9b65d159d97773877694fe0410228ebdf287aeeb 100644
--- a/Source/modules/webmidi/MIDIOutputMap.cpp
+++ b/Source/modules/webmidi/MIDIOutputMap.cpp
@@ -15,12 +15,4 @@ MIDIOutputMap::MIDIOutputMap(HeapHashMap<String, Member<MIDIOutput>> map)
 {
 }
 
-ScriptValue MIDIOutputMap::getForBinding(ScriptState* scriptState, const String& id)
-{
-    MIDIOutput* result = get(id);
-    if (result)
-        return ScriptValue(scriptState, toV8(result, scriptState->context()->Global(), scriptState->isolate()));
-    return ScriptValue(scriptState, v8::Undefined(scriptState->isolate()));
-}
-
 } // namespace blink