Bug 1529581 - Improve MediaTimer accuracy. r=padenot

Differential Revision: https://phabricator.services.mozilla.com/D129655

dom/media/MediaTimer.cpp

@@ -181,17 +181,12 @@ void MediaTimer::ArmTimer(const TimeStamp& aTarget, const TimeStamp& aNow) {
   MOZ_DIAGNOSTIC_ASSERT(!TimerIsArmed());
   MOZ_DIAGNOSTIC_ASSERT(aTarget > aNow);
 
-  // XPCOM timer resolution is in milliseconds. It's important to never resolve
-  // a timer when mTarget might compare < now (even if very close), so round up.
-  unsigned long delay = std::ceil((aTarget - aNow).ToMilliseconds());
-  TIMER_LOG("MediaTimer::ArmTimer delay=%lu", delay);
+  const TimeDuration delay = aTarget - aNow;
+  TIMER_LOG("MediaTimer::ArmTimer delay=%.3fms", delay.ToMilliseconds());
   mCurrentTimerTarget = aTarget;
-  nsresult rv = mTimer->InitWithNamedFuncCallback(&TimerCallback, this, delay,
-                                                  nsITimer::TYPE_ONE_SHOT,
-                                                  "MediaTimer::TimerCallback");
-  MOZ_DIAGNOSTIC_ASSERT(NS_SUCCEEDED(rv));
-  Unused << rv;
-  (void)rv;
+  MOZ_ALWAYS_SUCCEEDS(mTimer->InitHighResolutionWithNamedFuncCallback(
+      &TimerCallback, this, delay, nsITimer::TYPE_ONE_SHOT,
+      "MediaTimer::TimerCallback"));
 }
 
 }  // namespace mozilla