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

webrtc/base/fakeclock.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.
  */
 
 #include "webrtc/base/fakeclock.h"
 
 #include "webrtc/base/checks.h"
 #include "webrtc/base/messagequeue.h"
 
 namespace rtc {
 
-uint64_t FakeClock::TimeNanos() const {
+int64_t FakeClock::TimeNanos() const {
   CritScope cs(&lock_);
   return time_;
 }
 
-void FakeClock::SetTimeNanos(uint64_t nanos) {
+void FakeClock::SetTimeNanos(int64_t nanos) {
   {
     CritScope cs(&lock_);
     RTC_DCHECK(nanos >= time_);
     time_ = nanos;
   }
   // If message queues are waiting in a socket select() with a timeout provided
   // by the OS, they should wake up and dispatch all messages that are ready.
   MessageQueueManager::ProcessAllMessageQueues();
 }
 
 void FakeClock::AdvanceTime(TimeDelta delta) {
   {
     CritScope cs(&lock_);
     time_ += delta.ToNanoseconds();
   }
   MessageQueueManager::ProcessAllMessageQueues();
 }
 
 ScopedFakeClock::ScopedFakeClock() {
   prev_clock_ = SetClockForTesting(this);
 }
 
 ScopedFakeClock::~ScopedFakeClock() {
   SetClockForTesting(prev_clock_);
 }
 
 }  // namespace rtc