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

webrtc/api/stats/rtcstatsreport.h

Index: webrtc/api/stats/rtcstatsreport.h
diff --git a/webrtc/api/stats/rtcstatsreport.h b/webrtc/api/stats/rtcstatsreport.h
index 0ad7396121f8bd3252624b6da652349ce5568f2d..3efe6c9510678cb7f5d314fc9c17efbf9265907a 100644
--- a/webrtc/api/stats/rtcstatsreport.h
+++ b/webrtc/api/stats/rtcstatsreport.h
@@ -81,9 +81,9 @@ class RTCStatsReport : public rtc::RefCountInterface {
     return stats_of_type;
   }
 
-  // Creates a human readable string representation of the report, listing all
-  // of its stats objects.
-  std::string ToString() const;
+  // Creates a JSON readable string representation of the report,
+  // listing all of its stats objects.
+  std::string ToJson() const;
 
   friend class rtc::RefCountedObject<RTCStatsReport>;