Add a default implementation in metrics_default.cc of histograms methods in system_wrappers/interfac

webrtc/video/send_delay_stats_unittest.cc

Index: webrtc/video/send_delay_stats_unittest.cc
diff --git a/webrtc/video/send_delay_stats_unittest.cc b/webrtc/video/send_delay_stats_unittest.cc
index 44c62c3a452d84227f5bc43e1c10b24321d1e9bc..ec9c05ce832670689240745d4de6196f05f8e6df 100644
--- a/webrtc/video/send_delay_stats_unittest.cc
+++ b/webrtc/video/send_delay_stats_unittest.cc
@@ -12,7 +12,7 @@
 
 #include "testing/gtest/include/gtest/gtest.h"
 #include "webrtc/system_wrappers/include/metrics.h"
-#include "webrtc/test/histogram.h"
+#include "webrtc/system_wrappers/include/metrics_default.h"
 
 namespace webrtc {
 namespace {
@@ -102,7 +102,8 @@ TEST_F(SendDelayStatsTest, OldPacketsRemoved) {
 }
 
 TEST_F(SendDelayStatsTest, HistogramsAreUpdated) {
-  test::ClearHistograms();
+  metrics::Reset();
+  metrics::Enable();
   const int64_t kDelayMs1 = 5;
   const int64_t kDelayMs2 = 10;
   uint16_t id = 0;
@@ -115,8 +116,9 @@ TEST_F(SendDelayStatsTest, HistogramsAreUpdated) {
     EXPECT_TRUE(OnSentPacket(id));
   }
   stats_.reset();
-  EXPECT_EQ(2, test::NumHistogramSamples("WebRTC.Video.SendDelayInMs"));
-  EXPECT_EQ(kDelayMs2, test::LastHistogramSample("WebRTC.Video.SendDelayInMs"));
+  EXPECT_EQ(2, metrics::NumSamples("WebRTC.Video.SendDelayInMs"));
+  EXPECT_EQ(1, metrics::NumEvents("WebRTC.Video.SendDelayInMs", kDelayMs1));
+  EXPECT_EQ(1, metrics::NumEvents("WebRTC.Video.SendDelayInMs", kDelayMs2));
 }
 
 }  // namespace webrtc