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

webrtc/sdk/sdk.gyp

 # Copyright 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.
 
 {
   'includes': [
@@ skipping 58 matching lines @@
               ],
             }],
           ],
         },
         {
           'target_name': 'rtc_sdk_peerconnection_objc',
           'type': 'static_library',
           'includes': [ '../build/objc_common.gypi' ],
           'dependencies': [
             '<(webrtc_root)/api/api.gyp:libjingle_peerconnection',
+            '<(webrtc_root)/system_wrappers/system_wrappers.gyp:metrics_default',
             'rtc_sdk_common_objc',
           ],
           'include_dirs': [
             'objc/Framework/Classes',
             'objc/Framework/Headers',
           ],
           'direct_dependent_settings': {
             'include_dirs': [
               'objc/Framework/Classes',
               'objc/Framework/Headers',
@@ skipping 131 matching lines @@
             'objc/Framework/Headers/WebRTC/RTCSSLAdapter.h',
             'objc/Framework/Headers/WebRTC/RTCTracing.h',
             'objc/Framework/Headers/WebRTC/WebRTC.h',
             'objc/Framework/Modules/module.modulemap',
           ],
           'mac_framework_headers': [
             '<!@(find -E objc/Framework/Headers -regex ".*(h)")',
           ],
           'dependencies': [
             '<(webrtc_root)/system_wrappers/system_wrappers.gyp:field_trial_default',
+            '<(webrtc_root)/system_wrappers/system_wrappers.gyp:metrics_default',
             'rtc_sdk_peerconnection_objc',
           ],
           'xcode_settings': {
             'CODE_SIGNING_REQUIRED': 'NO',
             'CODE_SIGN_IDENTITY': '',
             'DEFINES_MODULE': 'YES',
             'INFOPLIST_FILE': 'objc/Framework/Info.plist',
             'LD_DYLIB_INSTALL_NAME': '@rpath/WebRTC.framework/WebRTC',
             'MODULEMAP_FILE': '<(webrtc_root)/sdk/Framework/Modules/module.modulemap',
           },
@@ skipping 22 matching lines @@
               'mac_framework_headers!': [
                 'objc/Framework/Headers/WebRTC/RTCFileLogger.h',
               ],
             }],
           ],  # conditions
         }, # rtc_sdk_framework_objc
       ],  # targets
     }],  # OS=="ios" or (OS=="mac" and mac_deployment_target=="10.7")
   ],
 }