Change rtc::TimeNanos and rtc::TimeMicros return value from uint64_t to int64_t.

webrtc/stats/rtcstatsreport.cc

 /*
  *  Copyright 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 39 matching lines @@
     const RTCStatsReport::ConstIterator& other) const {
   return it_ == other.it_;
 }
 
 bool RTCStatsReport::ConstIterator::operator!=(
     const RTCStatsReport::ConstIterator& other) const {
   return !(*this == other);
 }
 
 rtc::scoped_refptr<RTCStatsReport> RTCStatsReport::Create(
-    uint64_t timestamp_us) {
+    int64_t timestamp_us) {
   return rtc::scoped_refptr<RTCStatsReport>(
       new rtc::RefCountedObject<RTCStatsReport>(timestamp_us));
 }
 
-RTCStatsReport::RTCStatsReport(uint64_t timestamp_us)
+RTCStatsReport::RTCStatsReport(int64_t timestamp_us)
     : timestamp_us_(timestamp_us) {
 }
 
 RTCStatsReport::~RTCStatsReport() {
 }
 
 bool RTCStatsReport::AddStats(std::unique_ptr<const RTCStats> stats) {
   return !stats_.insert(std::make_pair(std::string(stats->id()),
                         std::move(stats))).second;
 }
@@ skipping 30 matching lines @@
   if (it != end()) {
     oss << it->ToString();
     for (++it; it != end(); ++it) {
       oss << '\n' << it->ToString();
     }
   }
   return oss.str();
 }
 
 }  // namespace webrtc