MediaStream API: Changing the device enumeration to be async

Source/modules/modules.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
     # ways.
     'extra_blink_module_idl_files': [],
     'extra_blink_module_files': [],
 
@@ skipping 57 matching lines @@
       'indexeddb/IDBVersionChangeEvent.idl',
       'indexeddb/WorkerContextIndexedDatabase.idl',
       'mediasource/DOMWindowMediaSource.idl',
       'mediasource/WebKitMediaSource.idl',
       'mediasource/WebKitSourceBuffer.idl',
       'mediasource/WebKitSourceBufferList.idl',
       'mediastream/MediaStream.idl',
       'mediastream/MediaStreamEvent.idl',
       'mediastream/MediaStreamTrack.idl',
       'mediastream/MediaStreamTrackEvent.idl',
+      'mediastream/MediaStreamTrackSourcesCallback.idl',
       'mediastream/NavigatorMediaStream.idl',
       'mediastream/NavigatorUserMediaError.idl',
       'mediastream/NavigatorUserMediaErrorCallback.idl',
       'mediastream/NavigatorUserMediaSuccessCallback.idl',
       'mediastream/RTCDTMFSender.idl',
       'mediastream/RTCDTMFToneChangeEvent.idl',
       'mediastream/RTCDataChannel.idl',
       'mediastream/RTCDataChannelEvent.idl',
       'mediastream/RTCErrorCallback.idl',
       'mediastream/RTCIceCandidate.idl',
@@ skipping 259 matching lines @@
       'mediastream/MediaStream.cpp',
       'mediastream/MediaStream.h',
       'mediastream/MediaStreamEvent.cpp',
       'mediastream/MediaStreamEvent.h',
       'mediastream/MediaStreamRegistry.cpp',
       'mediastream/MediaStreamRegistry.h',
       'mediastream/MediaStreamTrack.cpp',
       'mediastream/MediaStreamTrack.h',
       'mediastream/MediaStreamTrackEvent.cpp',
       'mediastream/MediaStreamTrackEvent.h',
+      'mediastream/MediaStreamTrackSourcesCallback.h',
+      'mediastream/MediaStreamTrackSourcesRequestImpl.cpp',
+      'mediastream/MediaStreamTrackSourcesRequestImpl.h',
       'mediastream/NavigatorMediaStream.cpp',
       'mediastream/NavigatorMediaStream.h',
       'mediastream/NavigatorUserMediaError.h',
       'mediastream/NavigatorUserMediaErrorCallback.h',
       'mediastream/NavigatorUserMediaSuccessCallback.h',
       'mediastream/RTCDTMFSender.cpp',
       'mediastream/RTCDTMFSender.h',
       'mediastream/RTCDTMFToneChangeEvent.cpp',
       'mediastream/RTCDTMFToneChangeEvent.h',
       'mediastream/RTCDataChannel.cpp',
@@ skipping 289 matching lines @@
       'websockets/WorkerThreadableWebSocketChannel.cpp',
       'websockets/WorkerThreadableWebSocketChannel.h',
     ],
     'modules_unittest_files': [
       'websockets/WebSocketDeflaterTest.cpp',
       'websockets/WebSocketExtensionDispatcherTest.cpp',
       'websockets/WebSocketPerMessageDeflateTest.cpp',
     ],
   },
 }