When using clang, switch on -Wc++11-narrowing

webrtc/modules/video_coding/frame_buffer2_unittest.cc

 /*
  *  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.
  */
 
@@ skipping 135 matching lines @@
   }
 
   template <typename... T>
   int InsertFrame(uint16_t picture_id,
                   uint8_t spatial_layer,
                   int64_t ts_ms,
                   bool inter_layer_predicted,
                   T... refs) {
     static_assert(sizeof...(refs) <= kMaxReferences,
                   "To many references specified for FrameObject.");
-    std::array<uint16_t, sizeof...(refs)> references = {{refs...}};
+    std::array<uint16_t, sizeof...(refs)> references = {
+        {rtc::checked_cast<uint16_t>(refs)...}};
 
     std::unique_ptr<FrameObjectFake> frame(new FrameObjectFake());
     frame->picture_id = picture_id;
     frame->spatial_layer = spatial_layer;
     frame->timestamp = ts_ms * 90;
     frame->num_references = references.size();
     frame->inter_layer_predicted = inter_layer_predicted;
     for (size_t r = 0; r < references.size(); ++r)
       frame->references[r] = references[r];
 
@@ skipping 382 matching lines @@
   ExtractFrame(0, true);
   ExtractFrame();
 
   CheckFrame(0, 1, 0);
   CheckFrame(1, 3, 0);
   CheckNoFrame(2);
 }
 
 }  // namespace video_coding
 }  // namespace webrtc