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..770ebcde848e947b413ec21d13765c5f04b4a04b 100644
--- a/Source/modules/webmidi/MIDIOutputMap.cpp
+++ b/Source/modules/webmidi/MIDIOutputMap.cpp
@@ -5,7 +5,6 @@
 #include "config.h"
 #include "modules/webmidi/MIDIOutputMap.h"
 
-#include "bindings/core/v8/ScriptState.h"
 #include "bindings/modules/v8/V8MIDIOutput.h"
 
 namespace blink {
@@ -15,12 +14,4 @@ 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