Bug 1608931 - followup: fix subtle unintended behavior change.

This can fire in some tests that take over the refresh driver via script.

Differential Revision: https://phabricator.services.mozilla.com/D60620

--HG--
extra : moz-landing-system : lando

layout/base/nsRefreshDriver.cpp

@@ -1913,7 +1913,8 @@ void nsRefreshDriver::Tick(VsyncId aId, TimeStamp aNowTime) {
 
   mResizeSuppressed = false;
 
-  auto restoreInRefresh = MakeScopeExit([&] { mInRefresh = false; });
+  bool oldInRefresh = mInRefresh;
+  auto restoreInRefresh = MakeScopeExit([&] { mInRefresh = oldInRefresh; });
   mInRefresh = true;
 
   AutoRestore<TimeStamp> restoreTickStart(mTickStart);