Use swap instead of copy in RtcHistogram::GetAndReset.

webrtc/system_wrappers/source/metrics_default_unittest.cc

 /*
  *  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.
  */
 
@@ skipping 116 matching lines @@
   metrics::GetAndReset(&histograms);
   EXPECT_EQ(2u, histograms.size());
   EXPECT_EQ(0, metrics::NumSamples("Histogram1"));
   EXPECT_EQ(0, metrics::NumSamples("Histogram2"));
 
   EXPECT_EQ(3, NumSamples("Histogram1", histograms));
   EXPECT_EQ(1, NumSamples("Histogram2", histograms));
   EXPECT_EQ(1, NumEvents("Histogram1", 4, histograms));
   EXPECT_EQ(2, NumEvents("Histogram1", 5, histograms));
   EXPECT_EQ(1, NumEvents("Histogram2", 10, histograms));
+
+  // Add samples after reset.
+  metrics::GetAndReset(&histograms);
+  EXPECT_EQ(0u, histograms.size());
+  RTC_HISTOGRAM_PERCENTAGE("Histogram1", 50);
+  RTC_HISTOGRAM_PERCENTAGE("Histogram2", 8);
+  EXPECT_EQ(1, metrics::NumSamples("Histogram1"));
+  EXPECT_EQ(1, metrics::NumSamples("Histogram2"));
+  EXPECT_EQ(1, metrics::NumEvents("Histogram1", 50));
+  EXPECT_EQ(1, metrics::NumEvents("Histogram2", 8));
 }
 
 TEST_F(MetricsDefaultTest, TestMinMaxBucket) {
   const std::string kName = "MinMaxCounts100";
   RTC_HISTOGRAM_COUNTS_100(kName, 4);
 
   std::map<std::string, std::unique_ptr<metrics::SampleInfo>> histograms;
   metrics::GetAndReset(&histograms);
   EXPECT_EQ(1u, histograms.size());
   EXPECT_EQ(kName, histograms.begin()->second->name);
   EXPECT_EQ(1, histograms.begin()->second->min);
   EXPECT_EQ(100, histograms.begin()->second->max);
   EXPECT_EQ(50u, histograms.begin()->second->bucket_count);
   EXPECT_EQ(1u, histograms.begin()->second->samples.size());
 }
 
 }  // namespace webrtc