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

webrtc/base/timeutils.cc

Index: webrtc/base/timeutils.cc
diff --git a/webrtc/base/timeutils.cc b/webrtc/base/timeutils.cc
index 658d0796adad16dd1663621a14aa65362c7962ea..c424f701f77fc2b642d4f25429f6d1aaf3e93811 100644
--- a/webrtc/base/timeutils.cc
+++ b/webrtc/base/timeutils.cc
@@ -39,7 +39,7 @@ ClockInterface* SetClockForTesting(ClockInterface* clock) {
   return prev;
 }
 
-uint64_t SystemTimeNanos() {
+int64_t SystemTimeNanos() {
   int64_t ticks;
 #if defined(WEBRTC_MAC)
   static mach_timebase_info_data_t timebase;
@@ -88,7 +88,7 @@ int64_t SystemTimeMillis() {
   return static_cast<int64_t>(SystemTimeNanos() / kNumNanosecsPerMillisec);
 }
 
-uint64_t TimeNanos() {
+int64_t TimeNanos() {
   if (g_clock) {
     return g_clock->TimeNanos();
   }
@@ -100,11 +100,11 @@ uint32_t Time32() {
 }
 
 int64_t TimeMillis() {
-  return static_cast<int64_t>(TimeNanos() / kNumNanosecsPerMillisec);
+  return TimeNanos() / kNumNanosecsPerMillisec;
 }
 
-uint64_t TimeMicros() {
-  return static_cast<uint64_t>(TimeNanos() / kNumNanosecsPerMicrosec);
+int64_t TimeMicros() {
+  return TimeNanos() / kNumNanosecsPerMicrosec;
 }
 
 int64_t TimeAfter(int64_t elapsed) {