Add WebKit prefix to MediaSource,SourceBuffer, and SourceBufferList objects.

Source/modules/modules.gypi

 {
   'variables': {
     'modules_idl_files': [
       'battery/BatteryManager.idl',
       'battery/NavigatorBattery.idl',
       'device_orientation/DeviceAcceleration.idl',
       'device_orientation/DeviceMotionEvent.idl',
       'device_orientation/DeviceRotationRate.idl',
       'donottrack/NavigatorDoNotTrack.idl',
       'filesystem/DOMFileSystem.idl',
@@ skipping 39 matching lines @@
       'indexeddb/IDBDatabase.idl',
       'indexeddb/IDBFactory.idl',
       'indexeddb/IDBIndex.idl',
       'indexeddb/IDBKeyRange.idl',
       'indexeddb/IDBObjectStore.idl',
       'indexeddb/IDBOpenDBRequest.idl',
       'indexeddb/IDBRequest.idl',
       'indexeddb/IDBTransaction.idl',
       'indexeddb/IDBVersionChangeEvent.idl',
       'indexeddb/WorkerContextIndexedDatabase.idl',
-      'mediasource/MediaSource.idl',
-      'mediasource/SourceBuffer.idl',
-      'mediasource/SourceBufferList.idl',
+      'mediasource/WebKitMediaSource.idl',
+      'mediasource/WebKitSourceBuffer.idl',
+      'mediasource/WebKitSourceBufferList.idl',
       'mediastream/MediaStream.idl',
       'mediastream/MediaStreamEvent.idl',
       'mediastream/MediaStreamTrack.idl',
       'mediastream/MediaStreamTrackEvent.idl',
       'mediastream/NavigatorMediaStream.idl',
       'mediastream/NavigatorUserMediaError.idl',
       'mediastream/NavigatorUserMediaErrorCallback.idl',
       'mediastream/NavigatorUserMediaSuccessCallback.idl',
       'mediastream/RTCDTMFSender.idl',
       'mediastream/RTCDTMFToneChangeEvent.idl',
@@ skipping 248 matching lines @@
       'indexeddb/IDBTransactionCoordinator.h',
       'indexeddb/IDBVersionChangeEvent.cpp',
       'indexeddb/IDBVersionChangeEvent.h',
       'indexeddb/IndexedDB.h',
       'indexeddb/PageGroupIndexedDatabase.cpp',
       'indexeddb/PageGroupIndexedDatabase.h',
       'indexeddb/WorkerContextIndexedDatabase.cpp',
       'indexeddb/WorkerContextIndexedDatabase.h',
       'indexeddb/chromium/IDBFactoryBackendInterfaceChromium.cpp',
       'indexeddb/chromium/IDBFactoryBackendInterfaceChromium.h',
-      'mediasource/MediaSource.cpp',
-      'mediasource/MediaSource.h',
       'mediasource/MediaSourceRegistry.cpp',
       'mediasource/MediaSourceRegistry.h',
-      'mediasource/SourceBuffer.cpp',
-      'mediasource/SourceBuffer.h',
-      'mediasource/SourceBufferList.cpp',
-      'mediasource/SourceBufferList.h',
+      'mediasource/WebKitMediaSource.cpp',
+      'mediasource/WebKitMediaSource.h',
+      'mediasource/WebKitSourceBuffer.cpp',
+      'mediasource/WebKitSourceBuffer.h',
+      'mediasource/WebKitSourceBufferList.cpp',
+      'mediasource/WebKitSourceBufferList.h',
       'mediastream/MediaConstraintsImpl.cpp',
       'mediastream/MediaConstraintsImpl.h',
       'mediastream/MediaStream.cpp',
       'mediastream/MediaStream.h',
       'mediastream/MediaStreamEvent.cpp',
       'mediastream/MediaStreamEvent.h',
       'mediastream/MediaStreamRegistry.cpp',
       'mediastream/MediaStreamRegistry.h',
       'mediastream/MediaStreamTrack.cpp',
       'mediastream/MediaStreamTrack.h',
@@ skipping 287 matching lines @@
       'websockets/WebSocketHandshakeRequest.h',
       'websockets/WebSocketHandshakeResponse.cpp',
       'websockets/WebSocketHandshakeResponse.h',
       'websockets/WebSocketPerMessageDeflate.cpp',
       'websockets/WebSocketPerMessageDeflate.h',
       'websockets/WorkerThreadableWebSocketChannel.cpp',
       'websockets/WorkerThreadableWebSocketChannel.h',
     ],
   },
 }