Introduce MIDIInputMap and MIDIOutputMap.

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 177 matching lines @@
       'webdatabase/SQLStatementErrorCallback.idl',
       'webdatabase/SQLTransaction.idl',
       'webdatabase/SQLTransactionCallback.idl',
       'webdatabase/SQLTransactionErrorCallback.idl',
       'webdatabase/SQLTransactionSync.idl',
       'webdatabase/SQLTransactionSyncCallback.idl',
       'webmidi/MIDIAccess.idl',
       'webmidi/MIDIConnectionEvent.idl',
       'webmidi/MIDIErrorCallback.idl',
       'webmidi/MIDIInput.idl',
+      'webmidi/MIDIInputMap.idl',
       'webmidi/MIDIMessageEvent.idl',
       'webmidi/MIDIOutput.idl',
+      'webmidi/MIDIOutputMap.idl',
       'webmidi/MIDIPort.idl',
       'webmidi/MIDISuccessCallback.idl',
       'websockets/CloseEvent.idl',
       'websockets/WebSocket.idl',
     ],
     # 'partial interface' or target (right side of) 'implements'
     'modules_dependency_idl_files': [
       'battery/NavigatorBattery.idl',
       'beacon/NavigatorBeacon.idl',
       'credentialmanager/NavigatorCredentials.idl',
@@ skipping 736 matching lines @@
       'webmidi/MIDIClient.h',
       'webmidi/MIDIClientMock.cpp',
       'webmidi/MIDIClientMock.h',
       'webmidi/MIDIConnectionEvent.cpp',
       'webmidi/MIDIConnectionEvent.h',
       'webmidi/MIDIController.cpp',
       'webmidi/MIDIController.h',
       'webmidi/MIDIErrorCallback.h',
       'webmidi/MIDIInput.cpp',
       'webmidi/MIDIInput.h',
+      'webmidi/MIDIInputMap.cpp',
+      'webmidi/MIDIInputMap.h',
       'webmidi/MIDIMessageEvent.h',
+      'webmidi/MIDIPortMap.h',
       'webmidi/MIDIOptions.h',
       'webmidi/MIDIOutput.cpp',
       'webmidi/MIDIOutput.h',
+      'webmidi/MIDIOutputMap.cpp',
+      'webmidi/MIDIOutputMap.h',
       'webmidi/MIDIPort.cpp',
       'webmidi/MIDIPort.h',
       'webmidi/MIDISuccessCallback.h',
       'webmidi/NavigatorWebMIDI.cpp',
       'webmidi/NavigatorWebMIDI.h',
       'websockets/CloseEvent.h',
       'websockets/DOMWebSocket.cpp',
       'websockets/DOMWebSocket.h',
       'websockets/MainThreadWebSocketChannel.cpp',
       'websockets/MainThreadWebSocketChannel.h',
@@ skipping 50 matching lines @@
       'serviceworkers/ServiceWorkerContainerTest.cpp',
       'websockets/DOMWebSocketTest.cpp',
       'websockets/NewWebSocketChannelImplTest.cpp',
       'websockets/WebSocketDeflaterTest.cpp',
       'websockets/WebSocketExtensionDispatcherTest.cpp',
       'websockets/WebSocketExtensionParserTest.cpp',
       'websockets/WebSocketPerMessageDeflateTest.cpp',
     ],
   },
 }