Web MIDI: add dynamic MidiManager instantiation support for Linux

media/midi/midi_manager_mac_unittest.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "media/midi/midi_manager_mac.h"
 
 #include <CoreMIDI/MIDIServices.h>
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 94 matching lines @@
   MidiPortInfo info_;
   bool wait_for_port_;
   bool unexpected_callback_;
 
   DISALLOW_COPY_AND_ASSIGN(FakeMidiManagerClient);
 };
 
 class MidiManagerMacTest : public ::testing::Test {
  public:
   MidiManagerMacTest()
-      : manager_(new MidiManagerMac),
+      : manager_(new MidiManagerMac(nullptr)),
         message_loop_(new base::MessageLoop) {}
   ~MidiManagerMacTest() override {
     manager_->Shutdown();
     base::RunLoop run_loop;
     run_loop.RunUntilIdle();
   }
 
  protected:
   void StartSession(MidiManagerClient* client) {
     manager_->StartSession(client);
@@ skipping 40 matching lines @@
   EndSession(client.get());
   if (ep)
     MIDIEndpointDispose(ep);
   if (midi_client)
     MIDIClientDispose(midi_client);
 }
 
 }  // namespace
 
 }  // namespace midi