Make RTCStatsReport::ToString() return JSON-parseable string.

webrtc/stats/rtcstatsreport.cc

 /*
  *  Copyright 2016 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 89 matching lines @@
 
 RTCStatsReport::ConstIterator RTCStatsReport::end() const {
   return ConstIterator(rtc::scoped_refptr<const RTCStatsReport>(this),
                        stats_.cend());
 }
 
 std::string RTCStatsReport::ToString() const {
   std::ostringstream oss;
   ConstIterator it = begin();
   if (it != end()) {
-    oss << it->ToString();
+    oss << '[' << it->ToString();
     for (++it; it != end(); ++it) {
-      oss << '\n' << it->ToString();
+      oss << ",\n" << it->ToString();
     }
+    oss << ']';

[hbos, 2017/07/25 12:29:21]

Is it valid JSON to have just an array, and not a surrounding dictionary? Will
this be used for JSON parsing?

If it needs to be updated note that the stats report is a Map between stats IDs
and stats objects. Also note that this might affect the desired indentation of
the output string, if we still want to split it up into multiple lines.

Also note: the report also has a timestamp which currently is not included, but
it isn't in the spec so feel free to keep skipping it.

   }
   return oss.str();
 }
 
 }  // namespace webrtc