Web MIDI: add dynamic MidiManager instantiation support for Linux

content/browser/media/midi_host_unittest.cc

 // Copyright 2013 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 "content/browser/media/midi_host.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include "base/macros.h"
@@ skipping 30 matching lines @@
         timestamp(in_timestamp) {}
 
   MidiEventType type;
   uint32_t port_index;
   std::vector<uint8_t> data;
   double timestamp;
 };
 
 class FakeMidiManager : public midi::MidiManager {
  public:
+  FakeMidiManager() : MidiManager(nullptr) {}
   void DispatchSendMidiData(midi::MidiManagerClient* client,
                             uint32_t port_index,
                             const std::vector<uint8_t>& data,
                             double timestamp) override {
     events_.push_back(MidiEvent(DISPATCH_SEND_MIDI_DATA,
                                 port_index,
                                 data,
                                 timestamp));
   }
   std::vector<MidiEvent> events_;
@@ skipping 100 matching lines @@
   // Sending data to port 0 and 1 should be delivered now.
   OnSendData(port0);
   OnSendData(port1);
   RunLoopUntilIdle();
   EXPECT_EQ(3U, GetEventSize());
   CheckSendEventAt(1, port0);
   CheckSendEventAt(2, port1);
 }
 
 }  // namespace conent