Fix two UBSan warnings in NetEq

webrtc/modules/audio_coding/neteq/timestamp_scaler.cc

 /*
  *  Copyright (c) 2012 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 57 matching lines @@
     }
   }
 
   if (!(numerator_ == 1 && denominator_ == 1)) {
     // We have a scale factor != 1.
     if (!first_packet_received_) {
       external_ref_ = external_timestamp;
       internal_ref_ = external_timestamp;
       first_packet_received_ = true;
     }
-    int32_t external_diff = external_timestamp - external_ref_;
+    int64_t external_diff = external_timestamp - external_ref_;
     assert(denominator_ > 0);  // Should not be possible.
     external_ref_ = external_timestamp;
     internal_ref_ += (external_diff * numerator_) / denominator_;
     return internal_ref_;
   } else {
     // No scaling.
     return external_timestamp;
   }
 }
 
 
 uint32_t TimestampScaler::ToExternal(uint32_t internal_timestamp) const {
   if (!first_packet_received_ || (numerator_ == 1 && denominator_ == 1)) {
     // Not initialized, or scale factor is 1.
     return internal_timestamp;
   } else {
-    int32_t internal_diff = internal_timestamp - internal_ref_;
+    int64_t internal_diff = internal_timestamp - internal_ref_;
     assert(numerator_ > 0);  // Should not be possible.
     // Do not update references in this method.
     // Switch |denominator_| and |numerator_| to convert the other way.
     return external_ref_ + (internal_diff * denominator_) / numerator_;
   }
 }
 
 }  // namespace webrtc