GN: Change rtc_source_set targets --> rtc_static_library

webrtc/stats/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("../build/webrtc.gni")
 
 group("stats") {
   public_deps = [
     ":rtc_stats",
   ]
 }
 
 # GYP version: webrtc/stats/stats.gyp:rtc_stats
-rtc_source_set("rtc_stats") {
+rtc_static_library("rtc_stats") {
   cflags = []
   sources = [
     "rtcstats.cc",
     "rtcstats_objects.cc",
     "rtcstatsreport.cc",
   ]
 
   if (is_clang) {
     # Suppress warnings from the Chromium Clang plugin (bugs.webrtc.org/163).
     suppressed_configs += [ "//build/config/clang:find_bad_constructs" ]
@@ skipping 42 matching lines @@
       "../base:rtc_base_tests_utils",
       "../system_wrappers:metrics_default",
       "//testing/gmock",
     ]
 
     if (is_android) {
       deps += [ "//testing/android/native_test:native_test_native_code" ]
     }
   }
 }