Add Maplike<> utility mixin class for implementing maplike interfaces

Source/modules/webmidi/MIDIInputMap.cpp

Index: Source/modules/webmidi/MIDIInputMap.cpp
diff --git a/Source/modules/webmidi/MIDIInputMap.cpp b/Source/modules/webmidi/MIDIInputMap.cpp
index f6c72062e1992ff957d8ae7bf7b21174dbaa12fa..00b1505d3ba0bb02c171132f79a86f1220d25df4 100644
--- a/Source/modules/webmidi/MIDIInputMap.cpp
+++ b/Source/modules/webmidi/MIDIInputMap.cpp
@@ -15,13 +15,5 @@ MIDIInputMap::MIDIInputMap(const HeapHashMap<String, Member<MIDIInput>> map)
 {
 }
 
-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