Decoupling rtc_base from apple specific code [without cyclic deps]

webrtc/pc/BUILD.gn

 # Copyright (c) 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_android) {
@@ skipping 280 matching lines @@
       "../system_wrappers:metrics_default",
     ]
 
     if (rtc_build_libsrtp) {
       deps += [ "//third_party/libsrtp" ]
     }
 
     if (is_android) {
       deps += [ "//testing/android/native_test:native_test_support" ]
     }
+
+    if (is_ios || is_mac) {
+      deps += [ "../rtc_base:rtc_base_apple" ]
+    }
   }
 
   rtc_source_set("pc_test_utils") {
     testonly = true
     sources = [
       "test/fakeaudiocapturemodule.cc",
       "test/fakeaudiocapturemodule.h",
       "test/fakedatachannelprovider.h",
       "test/fakeperiodicvideocapturer.h",
       "test/fakertccertificategenerator.h",
@@ skipping 138 matching lines @@
       "../system_wrappers:metrics_default",
       "../test:audio_codec_mocks",
       "//testing/gmock",
     ]
 
     if (is_android) {
       deps += [ "//testing/android/native_test:native_test_support" ]
 
       shard_timeout = 900
     }
+
+    if (is_ios || is_mac) {
+      deps += [ "../rtc_base:rtc_base_apple" ]
+    }
   }
 }