refactor EnumerateDevices to make it a persistent request.

content/common/media/media_stream_options.cc

 // Copyright (c) 2012 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/common/media/media_stream_options.h"
 
 namespace media_stream {
 
 // static
 const int StreamDeviceInfo::kNoId = -1;
 
 StreamDeviceInfo::StreamDeviceInfo()
     : stream_type(content::MEDIA_STREAM_DEVICE_TYPE_NO_SERVICE),
       in_use(false),
       session_id(kNoId) {}
 
 StreamDeviceInfo::StreamDeviceInfo(MediaStreamType service_param,
                                    const std::string& name_param,
                                    const std::string& device_param,
                                    bool opened)
     : stream_type(service_param),
       name(name_param),
       device_id(device_param),
       in_use(opened),
       session_id(kNoId) {}
 
+// static
+bool StreamDeviceInfo::IsEqual(const StreamDeviceInfo& first,
+                               const StreamDeviceInfo& second) {
+  return first.stream_type == second.stream_type &&
+      first.name == second.name &&
+      first.device_id == second.device_id &&
+      first.in_use == second.in_use &&
+      first.session_id == second.session_id;
+}
+
 }  // namespace media_stream