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

webrtc/test/test.gyp

Index: webrtc/test/test.gyp
diff --git a/webrtc/test/test.gyp b/webrtc/test/test.gyp
index a04a128a0eb36bda096a987760a2c2f5854a293c..ac52e59f799dc57cdf80c90d4ece1d02d0d549e9 100644
--- a/webrtc/test/test.gyp
+++ b/webrtc/test/test.gyp
@@ -107,18 +107,6 @@
       ],
     },
     {
-      'target_name': 'histogram',
-      'type': 'static_library',
-      'sources': [
-        'histogram.cc',
-        'histogram.h',
-      ],
-      'dependencies': [
-        '<(webrtc_root)/common.gyp:webrtc_common',
-        '<(webrtc_root)/system_wrappers/system_wrappers.gyp:system_wrappers',
-      ],
-    },
-    {
       'target_name': 'test_main',
       'type': 'static_library',
       'sources': [
@@ -126,10 +114,10 @@
       ],
       'dependencies': [
         'field_trial',
-        'histogram',
         'test_support',
         '<(DEPTH)/testing/gtest.gyp:gtest',
         '<(DEPTH)/third_party/gflags/gflags.gyp:gflags',
+        '<(webrtc_root)/system_wrappers/system_wrappers.gyp:metrics_default',
       ],
     },
     {
@@ -178,11 +166,11 @@
       'type': 'static_library',
       'dependencies': [
         'field_trial',
-        'histogram',
         'test_support',
         '<(DEPTH)/testing/gmock.gyp:gmock',
         '<(DEPTH)/testing/gtest.gyp:gtest',
         '<(DEPTH)/third_party/gflags/gflags.gyp:gflags',
+        '<(webrtc_root)/system_wrappers/system_wrappers.gyp:metrics_default',
       ],
       'sources': [
         'run_all_unittests.cc',