Update libjingle's GN build config to match a recent fix.

third_party/libjingle/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/crypto.gni")
 
 # From third_party/libjingle/libjingle.gyp's target_defaults.
 config("jingle_unexported_configs") {
   defines = [
     "EXPAT_RELATIVE_PATH",
     "FEATURE_ENABLE_SSL",
     "GTEST_RELATIVE_PATH",
     "HAVE_SRTP",
     "HAVE_WEBRTC_VIDEO",
     "HAVE_WEBRTC_VOICE",
     "LOGGING_INSIDE_WEBRTC",
     "NO_MAIN_THREAD_WRAPPING",
     "NO_SOUND_SYSTEM",
     "SRTP_RELATIVE_PATH",
     "USE_WEBRTC_DEV_BRANCH",
     "ENABLE_EXTERNAL_AUTH",
+    "WEBRTC_CHROMIUM_BUILD",

[kjellander_chromium, 2014/08/30 17:01:52]

drive-by review: For the future, this should really be cleaned up and using the
webrtc:common_config and/or webrtc:common_inherited_config instead. Those config
targets sets the same defines as our common.gypi, as closely matching as
possible.

   ]
 
   include_dirs = [
     "overrides",
     "../../third_party/webrtc/overrides",
     "source",
     "../../testing/gtest/include",
     "../../third_party",
     "../../third_party/libyuv/include",
     "../../third_party/usrsctp",
@@ skipping 303 matching lines @@
   all_dependent_configs = [
     ":jingle_all_dependent_configs",
   ]
   if (is_win) {
     # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
     cflags = [ "/wd4309" ]
   }
 }
 
 # TODO(GYP): Port libjingle.gyp's enable_webrtc condition block.