Bug 1960303 - Remove layout.skip_ticks_while_page_suspended. r=smaug

Bug 1788125 introduced this, but now this is covered by
Document::IsRenderingSuppressed returning true if
!IsEventHandlingEnabled().

Differential Revision: https://phabricator.services.mozilla.com/D245399

dom/xhr/tests/test_bug1788125.html

@@ -27,8 +27,6 @@
   var didRunXHR = false;
 
   async function start() {
-    await SpecialPowers.pushPrefEnv({"set": [["layout.skip_ticks_while_page_suspended", true]]});
-
     window.addEventListener("animationiteration", function l() {
       ++animCount;
       info(animCount);

layout/base/nsRefreshDriver.cpp

@@ -2327,22 +2327,6 @@ void nsRefreshDriver::Tick(VsyncId aId, TimeStamp aNowTime,
     return;
   }
 
-  if (StaticPrefs::layout_skip_ticks_while_page_suspended()) {
-    Document* doc = mPresContext->Document();
-    nsGlobalWindowInner* win =
-        doc ? nsGlobalWindowInner::Cast(doc->GetInnerWindow()) : nullptr;
-    if (doc && doc->GetInnerWindow()) {
-      MOZ_ASSERT(nsGlobalWindowInner::Cast(doc->GetInnerWindow()));
-    }
-    // Synchronous DOM operations mark the document being in such. Window's
-    // suspend can be used also by external code. So we check here them both
-    // in order to limit rAF skipping to only those synchronous DOM APIs which
-    // also suspend window.
-    if (win && win->IsSuspended() && doc->IsInSyncOperation()) {
-      return;
-    }
-  }
-
   AUTO_PROFILER_LABEL_RELEVANT_FOR_JS("RefreshDriver tick", LAYOUT);
 
   nsAutoCString profilerStr;

modules/libpref/init/StaticPrefList.yaml

@@ -10396,13 +10396,6 @@
   value: true
   mirror: always
 
-# Pref to control whether to suspend also RefreshDriver::Tick when the page
-# itself is suspended because of some synchronous operation, like sync XHR.
-- name: layout.skip_ticks_while_page_suspended
-  type: bool
-  value: true
-  mirror: always
-
 # Pref to control how many consecutive scroll-anchoring adjustments (since the
 # most recent user scroll or timeout) we'll average, before we consider whether
 # to automatically turn off scroll anchoring. When we hit this threshold, the