Bug 1961687 - Stop starting the refresh driver timer from MostRecentRefresh(). r=smaug

Now this does a lot less, and I don't see a reason for needing it
anymore. I did a bit of auditing of the callers and they seem fine:

https://searchfox.org/mozilla-central/rev/29184ec2b107c8b9dd8c9a594711c27545dfb2c7/dom/animation/KeyframeEffect.cpp#1493
https://searchfox.org/mozilla-central/rev/29184ec2b107c8b9dd8c9a594711c27545dfb2c7/dom/animation/KeyframeEffect.cpp#671
https://searchfox.org/mozilla-central/rev/29184ec2b107c8b9dd8c9a594711c27545dfb2c7/dom/base/Document.cpp#17577

  We definitely don't want to trigger a tick from there.

https://searchfox.org/mozilla-central/rev/29184ec2b107c8b9dd8c9a594711c27545dfb2c7/dom/animation/DocumentTimeline.cpp#97

  We require already to call EnsureAnimationUpdate() to run that code
  next frame.

https://searchfox.org/mozilla-central/rev/29184ec2b107c8b9dd8c9a594711c27545dfb2c7/dom/smil/SMILAnimationController.cpp#41

  SMIL uses a refresh observer which keeps the driver ticking. See
  UpdateSampling().

https://searchfox.org/mozilla-central/rev/29184ec2b107c8b9dd8c9a594711c27545dfb2c7/dom/base/nsDOMWindowUtils.cpp#2946
https://searchfox.org/mozilla-central/rev/29184ec2b107c8b9dd8c9a594711c27545dfb2c7/layout/generic/ScrollContainerFrame.cpp#2475

  Test only, for manual refresh driver control which won't use the timer
  anyways.

https://searchfox.org/mozilla-central/rev/29184ec2b107c8b9dd8c9a594711c27545dfb2c7/layout/generic/ScrollContainerFrame.cpp#5872

  We're running a scroll event from the refresh driver.

https://searchfox.org/mozilla-central/rev/29184ec2b107c8b9dd8c9a594711c27545dfb2c7/layout/base/RestyleManager.cpp#3236-3238

  Just to work around this very thing (removed).

https://searchfox.org/mozilla-central/rev/29184ec2b107c8b9dd8c9a594711c27545dfb2c7/layout/generic/ScrollVelocityQueue.cpp#25

  For scroll snapping, no need to fire the refresh driver.

Differential Revision: https://phabricator.services.mozilla.com/D246141

dom/animation/Animation.cpp

@@ -1393,7 +1393,7 @@ static TimeStamp EnsurePaintIsScheduled(Document& aDoc) {
   if (!rd->IsInRefresh()) {
     return {};
   }
-  return rd->MostRecentRefresh(/* aEnsureTimerStarted = */ false);
+  return rd->MostRecentRefresh();
 }
 
 // https://drafts.csswg.org/web-animations/#play-an-animation

gfx/layers/AnimationInfo.cpp

@@ -513,8 +513,7 @@ void AnimationInfo::AddAnimationForProperty(
     if (readyTime.IsNull()) {
       // TODO(emilio): This should generally not happen anymore, can we remove
       // this SetPendingReadyTime call?
-      readyTime = aFrame->PresContext()->RefreshDriver()->MostRecentRefresh(
-          /* aEnsureTimerStarted= */ false);
+      readyTime = aFrame->PresContext()->RefreshDriver()->MostRecentRefresh();
       MOZ_ASSERT(!readyTime.IsNull());
       aAnimation->SetPendingReadyTime(readyTime);
     }

layout/base/RestyleManager.cpp

@@ -3233,10 +3233,6 @@ void RestyleManager::DoProcessPendingRestyles(ServoTraversalFlags aFlags) {
   ServoStyleSet* styleSet = StyleSet();
   Document* doc = presContext->Document();
 
-  // Ensure the refresh driver is active during traversal to avoid mutating
-  // mActiveTimer and mMostRecentRefresh time.
-  presContext->RefreshDriver()->MostRecentRefresh();
-
   if (!doc->GetServoRestyleRoot()) {
     // This might post new restyles, so need to do it here. Don't do it if we're
     // already going to restyle tho, so that we don't potentially reflow with

layout/base/nsPresContext.cpp

@@ -2824,8 +2824,7 @@ void nsPresContext::NotifyContentfulPaint() {
                "We should only notify contentful paint during refresh "
                "driver ticks");
     if (!perf->HadFCPTimingEntry()) {
-      TimeStamp nowTime = rootPresContext->RefreshDriver()->MostRecentRefresh(
-          /* aEnsureTimerStarted */ false);
+      TimeStamp nowTime = rootPresContext->RefreshDriver()->MostRecentRefresh();
       MOZ_ASSERT(!nowTime.IsNull(),
                  "Most recent refresh timestamp should exist since we are in "
                  "a refresh driver tick");

layout/base/nsRefreshDriver.cpp

@@ -1497,16 +1497,6 @@ void nsRefreshDriver::RestoreNormalRefresh() {
   mPendingTransactions.Clear();
 }
 
-TimeStamp nsRefreshDriver::MostRecentRefresh(bool aEnsureTimerStarted) const {
-  // In case of stylo traversal, we have already activated the refresh driver in
-  // RestyleManager::ProcessPendingRestyles().
-  if (aEnsureTimerStarted && !ServoStyleSet::IsInServoTraversal()) {
-    const_cast<nsRefreshDriver*>(this)->EnsureTimerStarted();
-  }
-
-  return mMostRecentRefresh;
-}
-
 void nsRefreshDriver::AddRefreshObserver(nsARefreshObserver* aObserver,
                                          FlushType aFlushType,
                                          const char* aObserverDescription) {

layout/base/nsRefreshDriver.h

@@ -79,7 +79,7 @@ class nsRefreshDriver final : public mozilla::layers::TransactionIdAllocator,
    * ensure that multiple animations started during the same event off
    * the main event loop have the same start time.)
    */
-  mozilla::TimeStamp MostRecentRefresh(bool aEnsureTimerStarted = true) const;
+  mozilla::TimeStamp MostRecentRefresh() const { return mMostRecentRefresh; }
 
   /**
    * Add / remove refresh observers.