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

webrtc/sdk/sdk.gyp

Index: webrtc/sdk/sdk.gyp
diff --git a/webrtc/sdk/sdk.gyp b/webrtc/sdk/sdk.gyp
index 5f83b3297bea0fee78e172f53f63304583ea187a..1c8e4bd199ce7fd0d0ca9649b2c986f3085b6967 100644
--- a/webrtc/sdk/sdk.gyp
+++ b/webrtc/sdk/sdk.gyp
@@ -76,6 +76,7 @@
           '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': [
@@ -227,6 +228,7 @@
           ],
           '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': {