Add scoped class for overriding field trials.

webrtc/modules/remote_bitrate_estimator/overuse_detector_unittest.cc

 /*
  *  Copyright (c) 2012 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 585 matching lines @@
   int sigma_ms = 10;
   int unique_overuse = Run100000Samples(packets_per_frame, packet_size,
                                         frame_duration_ms, sigma_ms);
   EXPECT_EQ(0, unique_overuse);
   int frames_until_overuse = RunUntilOveruse(packets_per_frame, packet_size,
       frame_duration_ms, sigma_ms, drift_per_frame_ms);
   EXPECT_EQ(14, frames_until_overuse);
 }
 
 class OveruseDetectorExperimentTest : public OveruseDetectorTest {
+ public:
+  OveruseDetectorExperimentTest()
+      : override_field_trials_(
+            "WebRTC-AdaptiveBweThreshold/Enabled-0.01,0.00018/") {}
+
  protected:
   void SetUp() override {
-    test::InitFieldTrialsFromString(
-        "WebRTC-AdaptiveBweThreshold/Enabled-0.01,0.00018/");
     overuse_detector_.reset(new OveruseDetector(options_));
   }
 
-  void TearDown() override { test::InitFieldTrialsFromString(""); }
+  test::ScopedFieldTrials override_field_trials_;
 };
 
 TEST_F(OveruseDetectorExperimentTest, ThresholdAdapts) {
   const double kOffset = 0.21;
   double kTsDelta = 3000.0;
   int64_t now_ms = 0;
   int num_deltas = 60;
   const int kBatchLength = 10;
 
   // Pass in a positive offset and verify it triggers overuse.
@@ skipping 104 matching lines @@
     if (overuse_state == kBwOverusing) {
       overuse_detected = true;
     }
     ++num_deltas;
     now_ms += 5;
   }
   EXPECT_TRUE(overuse_detected);
 }
 }  // namespace testing
 }  // namespace webrtc