refactor EnumerateDevices to make it a persistent request.

content/common/media/media_stream_options.h

 // 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.
 
 #ifndef CONTENT_COMMON_MEDIA_MEDIA_STREAM_OPTIONS_H_
 #define CONTENT_COMMON_MEDIA_MEDIA_STREAM_OPTIONS_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 21 matching lines @@
 
 // StreamDeviceInfo describes information about a device.
 struct CONTENT_EXPORT StreamDeviceInfo {
   static const int kNoId;
 
   StreamDeviceInfo();
   StreamDeviceInfo(MediaStreamType service_param,
                    const std::string& name_param,
                    const std::string& device_param,
                    bool opened);
+  bool operator==(const StreamDeviceInfo &other) const;

[tommi (sloooow) - chröme, 2012/07/30 12:10:21]

See previous comments about this operator.

[wjia(left Chromium), 2012/08/01 01:28:59]

To explain why all fields are used for comparison:
1. there should be no question about |stream_type|, |name| and |device_id|.
2. for |in_use|, if a device has been opened by other clients since last
enumeration, this can be some useful information for the requester, e.g., the
requester can display only non-opened devices.
3. for |session_id|, it should be same value, i.e., kNoId.

For now, only EnumerateDevices operation is using this comparison.

 
   // Describes the capture type.
   MediaStreamType stream_type;
   // Friendly name of the device.
   std::string name;
   // Unique name of a device. Even if there are multiple devices with the same
   // friendly name connected to the computer, this will be unique.
   std::string device_id;
   // Set to true if the device has been opened, false otherwise.
   bool in_use;
   // Id for this capture session. Unique for all sessions of the same type.
   int session_id;
 };
 
 typedef std::vector<StreamDeviceInfo> StreamDeviceInfoArray;
 
 }  // namespace media_stream
 
 #endif  // CONTENT_COMMON_MEDIA_MEDIA_STREAM_OPTIONS_H_