[PROTOTYPE] ServiceWorker: Add ServiceWorkerMessageEvent impl.

Source/modules/modules.gypi

 {
   'includes': [
     '../core/core_generated.gypi',
     'modules_generated.gypi',
   ],
   'variables': {
     # Experimental hooks for embedder to provide extra IDL and source files.
     #
     # Note: this is not a supported API. If you rely on this, you will be broken
     # from time to time as the code generator changes in backward incompatible
@@ skipping 152 matching lines @@
       'quota/StorageQuotaCallback.idl',
       'quota/StorageUsageCallback.idl',
       'screen_orientation/ScreenOrientation.idl',
       'serviceworkers/Client.idl',
       'serviceworkers/Clients.idl',
       'serviceworkers/ExtendableEvent.idl',
       'serviceworkers/FetchEvent.idl',
       'serviceworkers/ServiceWorker.idl',
       'serviceworkers/ServiceWorkerContainer.idl',
       'serviceworkers/ServiceWorkerGlobalScope.idl',
+      'serviceworkers/ServiceWorkerMessageEvent.idl',
       'serviceworkers/ServiceWorkerRegistration.idl',
       'serviceworkers/WindowClient.idl',
       'speech/SpeechGrammar.idl',
       'speech/SpeechGrammarList.idl',
       'speech/SpeechRecognition.idl',
       'speech/SpeechRecognitionAlternative.idl',
       'speech/SpeechRecognitionError.idl',
       'speech/SpeechRecognitionEvent.idl',
       'speech/SpeechRecognitionResult.idl',
       'speech/SpeechRecognitionResultList.idl',
@@ skipping 143 matching lines @@
       'mediastream/RTCDTMFToneChangeEvent.idl',
       'mediastream/RTCDataChannelEvent.idl',
       'mediastream/RTCIceCandidateEvent.idl',
       'navigatorconnect/CrossOriginConnectEvent.idl',
       'notifications/NotificationEvent.idl',
       'presentation/AvailableChangeEvent.idl',
       'presentation/DefaultSessionStartEvent.idl',
       'push_messaging/PushEvent.idl',
       'serviceworkers/ExtendableEvent.idl',
       'serviceworkers/FetchEvent.idl',
+      'serviceworkers/ServiceWorkerMessageEvent.idl',
       'speech/SpeechRecognitionError.idl',
       'speech/SpeechRecognitionEvent.idl',
       'speech/SpeechSynthesisEvent.idl',
       'storage/StorageEvent.idl',
       'webaudio/AudioProcessingEvent.idl',
       'webaudio/OfflineAudioCompletionEvent.idl',
       'webmidi/MIDIConnectionEvent.idl',
       'webmidi/MIDIMessageEvent.idl',
       'websockets/CloseEvent.idl',
     ],
@@ skipping 768 matching lines @@
       'serviceworkers/ServiceWorkerContainerClient.cpp',
       'serviceworkers/ServiceWorkerContainerClient.h',
       'serviceworkers/ServiceWorkerWindowClient.cpp',
       'serviceworkers/ServiceWorkerWindowClient.h',
       'serviceworkers/ServiceWorkerError.cpp',
       'serviceworkers/ServiceWorkerError.h',
       'serviceworkers/ServiceWorkerGlobalScope.cpp',
       'serviceworkers/ServiceWorkerGlobalScope.h',
       'serviceworkers/ServiceWorkerGlobalScopeClient.cpp',
       'serviceworkers/ServiceWorkerGlobalScopeClient.h',
+      'serviceworkers/ServiceWorkerMessageEvent.cpp',
+      'serviceworkers/ServiceWorkerMessageEvent.h',
       'serviceworkers/ServiceWorkerRegistration.cpp',
       'serviceworkers/ServiceWorkerRegistration.h',
       'serviceworkers/ServiceWorkerScriptCachedMetadataHandler.cpp',
       'serviceworkers/ServiceWorkerScriptCachedMetadataHandler.h',
       'serviceworkers/ServiceWorkerThread.cpp',
       'serviceworkers/ServiceWorkerThread.h',
       'serviceworkers/WaitUntilObserver.cpp',
       'speech/DOMWindowSpeechSynthesis.cpp',
       'speech/DOMWindowSpeechSynthesis.h',
       'speech/SpeechGrammar.cpp',
@@ skipping 300 matching lines @@
       'webaudio/AudioBasicProcessorHandlerTest.cpp',
       'webaudio/ConvolverNodeTest.cpp',
       'webaudio/DynamicsCompressorNodeTest.cpp',
       'webaudio/ScriptProcessorNodeTest.cpp',
       'webaudio/StereoPannerNodeTest.cpp',
       'websockets/DOMWebSocketTest.cpp',
       'websockets/DocumentWebSocketChannelTest.cpp',
     ],
   },
 }