Enable the -Wundef warning for clang

webrtc/video/send_statistics_proxy_unittest.cc

 /*
  *  Copyright (c) 2013 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.
  */
 
 #include "webrtc/video/send_statistics_proxy.h"
 
 #include <map>
 #include <memory>
 #include <string>
 #include <vector>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/system_wrappers/include/metrics.h"
 #include "webrtc/system_wrappers/include/metrics_default.h"
 
 namespace webrtc {
 namespace {
 const uint32_t kFirstSsrc = 17;
 const uint32_t kSecondSsrc = 42;
 const uint32_t kFirstRtxSsrc = 18;
 const uint32_t kSecondRtxSsrc = 43;
 
@@ skipping 709 matching lines @@
 
   EXPECT_EQ(
       1, metrics::NumSamples("WebRTC.Video.Screenshare.FecBitrateSentInKbps"));
   EXPECT_EQ(1, metrics::NumEvents(
                    "WebRTC.Video.Screenshare.FecBitrateSentInKbps",
                    static_cast<int>((rtx_counters.fec.TotalBytes() * 2 * 8) /
                                     metrics::kMinRunTimeInSeconds / 1000)));
 }
 
 }  // namespace webrtc