Bug 1570212 - Convert layout.reflow.synthMouseMove to a static pref. r=heycam

Differential Revision: https://phabricator.services.mozilla.com/D40338

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

layout/base/PresShell.cpp

@@ -752,7 +752,6 @@ already_AddRefed<nsFrameSelection> PresShell::FrameSelection() {
 
 //----------------------------------------------------------------------
 
-static bool sSynthMouseMove = true;
 static uint32_t sNextPresShellId;
 
 /* static */
@@ -849,12 +848,6 @@ PresShell::PresShell()
 #endif
   mLastOSWake = mLoadBegin = TimeStamp::Now();
 
-  static bool addedSynthMouseMove = false;
-  if (!addedSynthMouseMove) {
-    Preferences::AddBoolVarCache(&sSynthMouseMove,
-                                 "layout.reflow.synthMouseMove", true);
-    addedSynthMouseMove = true;
-  }
   PointerEventHandler::Initialize();
 }
 
@@ -5336,7 +5329,7 @@ void PresShell::SetRenderingState(const RenderingState& aState) {
 }
 
 void PresShell::SynthesizeMouseMove(bool aFromScroll) {
-  if (!sSynthMouseMove) return;
+  if (!StaticPrefs::layout_reflow_synthMouseMove()) return;
 
   if (mPaintingSuppressed || !mIsActive || !mPresContext) {
     return;
@@ -9121,7 +9114,7 @@ void PresShell::DidDoReflow(bool aInterruptible) {
     mDocument->ScheduleResizeObserversNotification();
   }
 
-  if (sSynthMouseMove) {
+  if (StaticPrefs::layout_reflow_synthMouseMove()) {
     SynthesizeMouseMove(false);
   }
 

modules/libpref/init/StaticPrefList.yaml

@@ -4432,6 +4432,11 @@
   value: true
   mirror: once
 
+- name: layout.reflow.synthMouseMove
+  type: bool
+  value: true
+  mirror: always
+
 # This and code dependent on it should be removed once containerless scrolling looks stable.
 - name: layout.scroll.root-frame-containers
   type: RelaxedAtomicBool