[WIP][NotForLand]: Use Mojo for WebMIDI IPC

media/midi/midi_service.mojom

+module media;
+
+enum MidiResultMojo {
+  NOT_INITIALIZED = -1,
+  OK = 0,
+  NOT_SUPPORTED,
+  INITIALIZATION_ERROR,
+};
+
+struct MidiPortInfoMojo {
+  string id;
+  string manufacturer;
+  string name;
+  string version;
+};
+
+// Renderer -> Browser
+interface MidiService {
+  StartSession(MidiServiceClient client) => (MidiResultMojo result);
+  EndSession();
+  SendData(uint32 port, array<uint8> data, double timestamp);
+};
+
+// Browser -> Renderer
+interface MidiServiceClient {
+  AcknowledgeSentData(uint32 bytes_sent);
+  AddInputPort(MidiPortInfoMojo input_port);
+  AddOutputPort(MidiPortInfoMojo input_port);
+  DataReceived(uint32 port, array<uint8> data, double timestamp);
+};