refactor EnumerateDevices to make it a persistent request.

content/common/media/media_stream_options.h

Index: content/common/media/media_stream_options.h
===================================================================
--- content/common/media/media_stream_options.h	(revision 148913)
+++ content/common/media/media_stream_options.h	(working copy)
@@ -39,6 +39,7 @@
                    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;