[gcc 4.x] Initialize web_port_index to 0 to fix build error while using GCC 4.x toolchain.

media/midi/midi_manager_alsa.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_alsa.h"
 
 #include <alsa/asoundlib.h>
 #include <stdlib.h>
 #include <algorithm>
 #include <string>
@@ skipping 428 matching lines @@
     scoped_ptr<MidiPort> port) {
   ports()->push_back(port.Pass());
 }
 
 MidiManagerAlsa::MidiPortState::MidiPortState()
     : num_input_ports_(0), num_output_ports_(0) {
 }
 
 uint32 MidiManagerAlsa::MidiPortState::Insert(scoped_ptr<MidiPort> port) {
   // Add the web midi index.
-  uint32 web_port_index;
+  uint32 web_port_index = 0;
   switch (port->type()) {
     case MidiPort::Type::kInput:
       web_port_index = num_input_ports_++;
       break;
     case MidiPort::Type::kOutput:
       web_port_index = num_output_ports_++;
       break;
   }
   port->set_web_port_index(web_port_index);
   ports()->push_back(port.Pass());
@@ skipping 549 matching lines @@
   // Update our map.
   source_map_[AddrToInt(client_id, port_id)] = port_index;
   return true;
 }
 
 MidiManager* MidiManager::Create() {
   return new MidiManagerAlsa();
 }
 
 }  // namespace media