Trace loggging: Check for g_event_logger is not null before calling it.

webrtc/sdk/BUILD.gn

 # 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.
 
 import("../webrtc.gni")
 if (is_ios) {
@@ skipping 366 matching lines @@
           visibility = [ "..:rtc_unittests" ]
         }
         sources = [
           "objc/Framework/UnitTests/RTCConfigurationTest.mm",
           "objc/Framework/UnitTests/RTCDataChannelConfigurationTest.mm",
           "objc/Framework/UnitTests/RTCIceCandidateTest.mm",
           "objc/Framework/UnitTests/RTCIceServerTest.mm",
           "objc/Framework/UnitTests/RTCMediaConstraintsTest.mm",
           "objc/Framework/UnitTests/RTCPeerConnectionTest.mm",
           "objc/Framework/UnitTests/RTCSessionDescriptionTest.mm",
+          "objc/Framework/UnitTests/RTCTracingTest.mm",
           "objc/Framework/UnitTests/avformatmappertests.mm",
         ]
         if (is_ios &&
             !(use_ios_simulator &&
               # The tests crash on these simulator versions:
               (ios_sdk_version == "10.0" || ios_sdk_version == "10.1"))) {
           sources +=
               [ "objc/Framework/UnitTests/RTCCameraVideoCapturerTests.mm" ]
         }
 
@@ skipping 201 matching lines @@
         public_deps = [
           "$rtc_libyuv_dir",
         ]
       } else {
         # Need to add a directory normally exported by libyuv.
         include_dirs = [ "$rtc_libyuv_dir/include" ]
       }
     }
   }
 }