Convert third_party source sets to static libraries.

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/features.gni")
 
 # From third_party/libjingle/libjingle.gyp's target_defaults.
 config("jingle_unexported_configs") {
   defines = [
     "EXPAT_RELATIVE_PATH",
@@ skipping 214 matching lines @@
   }
 
   configs += [ ":jingle_unexported_configs" ]
   public_configs = [ ":jingle_public_configs" ]
 }
 
 if (enable_webrtc) {
   # TODO(kjellander): Move this target into //third_party/webrtc_overrides as
   # soon as the work in bugs.webrtc.org/4256 has gotten rid of the duplicated
   # source listings above.
-  source_set("libjingle_webrtc") {
+  static_library("libjingle_webrtc") {
     sources = [
       "../webrtc_overrides/init_webrtc.cc",
       "../webrtc_overrides/init_webrtc.h",
     ]
     configs += [ ":jingle_unexported_configs" ]
     public_configs = [ ":jingle_public_configs" ]
     public_deps = [
       ":libjingle_webrtc_common",
     ]
   }
 
-  source_set("libjingle_webrtc_common") {
+  static_library("libjingle_webrtc_common") {
     sources = [
       "../webrtc/api/audiotrack.cc",
       "../webrtc/api/audiotrack.h",
       "../webrtc/api/datachannel.cc",
       "../webrtc/api/datachannel.h",
       "../webrtc/api/dtmfsender.cc",
       "../webrtc/api/dtmfsender.h",
       "../webrtc/api/jsep.h",
       "../webrtc/api/jsepicecandidate.cc",
       "../webrtc/api/jsepicecandidate.h",
@@ skipping 133 matching lines @@
       "//third_party/libsrtp",
       "//third_party/usrsctp",
       "//third_party/webrtc",
       "//third_party/webrtc/modules/media_file",
       "//third_party/webrtc/modules/video_capture",
       "//third_party/webrtc/system_wrappers",
       "//third_party/webrtc/voice_engine",
     ]
   }
 
-  source_set("libstunprober") {
+  static_library("libstunprober") {
     p2p_dir = "../webrtc/p2p"
     sources = [
       "$p2p_dir/stunprober/stunprober.cc",
     ]
 
     deps = [
       ":libjingle_webrtc_common",
       "//third_party/webrtc/base:rtc_base",
     ]
   }
 }  # enable_webrtc