Wire up experiment for improved screenshare bwe.

webrtc/video/screenshare_loopback.cc

 /*
  *  Copyright (c) 2015 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 277 matching lines @@
 }  // namespace webrtc
 
 int main(int argc, char* argv[]) {
   ::testing::InitGoogleTest(&argc, argv);
   rtc::FlagList::SetFlagsFromCommandLine(&argc, argv, true);
   if (webrtc::flags::FLAG_help) {
     rtc::FlagList::Print(nullptr, false);
     return 0;
   }
 
-  webrtc::test::InitFieldTrialsFromString(
+  webrtc::test::ScopedFieldTrials field_trials(
       webrtc::flags::FLAG_force_fieldtrials);
   webrtc::test::RunTest(webrtc::Loopback);
   return 0;
 }