RTCStatsReport: Take ownership of other's stats with TakeMembersFrom

webrtc/stats/stats.gyp

 # Copyright (c) 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.
 
 {
   'includes': [ '../build/common.gypi', ],
@@ skipping 19 matching lines @@
           'target_name': 'rtc_stats_unittests',
           'type': '<(gtest_target_type)',
           'dependencies': [
             '<(DEPTH)/testing/gmock.gyp:gmock',
             '<(webrtc_root)/base/base_tests.gyp:rtc_base_tests_utils',
             '<(webrtc_root)/system_wrappers/system_wrappers.gyp:metrics_default',
             'rtc_stats',
           ],
           'sources': [
             'rtcstats_unittest.cc',
+            'rtcstatsreport_unittest.cc',
           ],
         },
       ],
     }],
   ],
 }