MidiManagerUsb should be able to accept multiple devices.

media/midi/midi_manager_usb.cc

 // Copyright 2014 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_usb.h"
 
 #include "base/callback.h"
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/message_loop/message_loop.h"
@@ skipping 65 matching lines @@
 }
 
 
 void MidiManagerUsb::OnEnumerateDevicesDone(bool result,
                                             UsbMidiDevice::Devices* devices) {
   if (!result) {
     initialize_callback_.Run(MIDI_INITIALIZATION_ERROR);
     return;
   }
   devices->swap(devices_);
+  std::vector<UsbMidiJack> input_jacks;
   for (size_t i = 0; i < devices_.size(); ++i) {
     UsbMidiDescriptorParser parser;
     std::vector<uint8> descriptor = devices_[i]->GetDescriptor();
     const uint8* data = descriptor.size() > 0 ? &descriptor[0] : NULL;
     std::vector<UsbMidiJack> jacks;
     bool parse_result = parser.Parse(devices_[i],
                                      data,
                                      descriptor.size(),
                                      &jacks);
     if (!parse_result) {
       initialize_callback_.Run(MIDI_INITIALIZATION_ERROR);
       return;
     }
-    std::vector<UsbMidiJack> input_jacks;
     for (size_t j = 0; j < jacks.size(); ++j) {
       if (jacks[j].direction() == UsbMidiJack::DIRECTION_OUT) {
         output_streams_.push_back(new UsbMidiOutputStream(jacks[j]));
         // TODO(yhirano): Set appropriate properties.
         // TODO(yhiran): Port ID should contain product ID / vendor ID.
         // Port ID must be unique in a MIDI manager. This (and the below) ID
         // setting is sufficiently unique although there is no user-friendly
         // meaning.
         MidiPortInfo port;
         port.id = base::StringPrintf("port-%ld-%ld",
                                      static_cast<long>(i),
                                      static_cast<long>(j));
         AddOutputPort(port);
       } else {
         DCHECK_EQ(jacks[j].direction(), UsbMidiJack::DIRECTION_IN);
         input_jacks.push_back(jacks[j]);
         // TODO(yhirano): Set appropriate properties.
         MidiPortInfo port;
         port.id = base::StringPrintf("port-%ld-%ld",
                                      static_cast<long>(i),
                                      static_cast<long>(j));
         AddInputPort(port);
       }
     }
-    input_stream_.reset(new UsbMidiInputStream(input_jacks, this));
   }
+  input_stream_.reset(new UsbMidiInputStream(input_jacks, this));
   initialize_callback_.Run(MIDI_OK);
 }
 
 }  // namespace media