Bug 1573268 - Convert two layout.idle-period.* prefs to static prefs. r=njn

Converts layout.idle_period.required_quiescent_frames and layout.idle_period.time_limit to static prefs. These are the last prefs in nsLayoutUtils::initialize(), but since the function still calls nsComputedDOMStyle::RegisterPrefChangeCallbacks() the commit retains it.

Differential Revision: https://phabricator.services.mozilla.com/D41856

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

layout/base/nsLayoutUtils.cpp

@@ -168,13 +168,6 @@ using namespace mozilla::gfx;
 using mozilla::dom::HTMLMediaElement_Binding::HAVE_METADATA;
 using mozilla::dom::HTMLMediaElement_Binding::HAVE_NOTHING;
 
-// The time in number of frames that we estimate for a refresh driver
-// to be quiescent
-#define DEFAULT_QUIESCENT_FRAMES 2
-// The time (milliseconds) we estimate is needed between the end of an
-// idle time and the next Tick.
-#define DEFAULT_IDLE_PERIOD_TIME_LIMIT 1.0f
-
 #ifdef DEBUG
 // TODO: remove, see bug 598468.
 bool nsLayoutUtils::gPreventAssertInCompareTreePosition = false;
@@ -183,11 +176,6 @@ bool nsLayoutUtils::gPreventAssertInCompareTreePosition = false;
 typedef ScrollableLayerGuid::ViewID ViewID;
 typedef nsStyleTransformMatrix::TransformReferenceBox TransformReferenceBox;
 
-/* static */
-uint32_t nsLayoutUtils::sIdlePeriodDeadlineLimit;
-/* static */
-uint32_t nsLayoutUtils::sQuiescentFramesBeforeIdlePeriod;
-
 static ViewID sScrollIdCounter = ScrollableLayerGuid::START_SCROLL_ID;
 
 typedef nsDataHashtable<nsUint64HashKey, nsIContent*> ContentMap;
@@ -7961,13 +7949,6 @@ size_t nsLayoutUtils::SizeOfTextRunsForFrames(nsIFrame* aFrame,
 
 /* static */
 void nsLayoutUtils::Initialize() {
-  Preferences::AddUintVarCache(&sIdlePeriodDeadlineLimit,
-                               "layout.idle_period.time_limit",
-                               DEFAULT_IDLE_PERIOD_TIME_LIMIT);
-  Preferences::AddUintVarCache(&sQuiescentFramesBeforeIdlePeriod,
-                               "layout.idle_period.required_quiescent_frames",
-                               DEFAULT_QUIESCENT_FRAMES);
-
   nsComputedDOMStyle::RegisterPrefChangeCallbacks();
 }
 

layout/base/nsLayoutUtils.h

@@ -2442,12 +2442,6 @@ class nsLayoutUtils {
 
   static bool FontSizeInflationEnabled(nsPresContext* aPresContext);
 
-  static uint32_t IdlePeriodDeadlineLimit() { return sIdlePeriodDeadlineLimit; }
-
-  static uint32_t QuiescentFramesBeforeIdlePeriod() {
-    return sQuiescentFramesBeforeIdlePeriod;
-  }
-
   /**
    * Returns true if the nglayout.debug.invalidation pref is set to true.
    */
@@ -2992,9 +2986,6 @@ class nsLayoutUtils {
       const nsIFrame* aFrame);
 
  private:
-  static uint32_t sIdlePeriodDeadlineLimit;
-  static uint32_t sQuiescentFramesBeforeIdlePeriod;
-
   /**
    * Helper function for LogTestDataForPaint().
    */

layout/base/nsRefreshDriver.cpp

@@ -271,13 +271,14 @@ class RefreshDriverTimer {
     TimeStamp idleEnd = mostRecentRefresh + refreshRate;
 
     if (idleEnd +
-            refreshRate * nsLayoutUtils::QuiescentFramesBeforeIdlePeriod() <
+            refreshRate *
+                StaticPrefs::layout_idle_period_required_quiescent_frames() <
         TimeStamp::Now()) {
       return aDefault;
     }
 
     idleEnd = idleEnd - TimeDuration::FromMilliseconds(
-                            nsLayoutUtils::IdlePeriodDeadlineLimit());
+                            StaticPrefs::layout_idle_period_time_limit());
     return idleEnd < aDefault ? idleEnd : aDefault;
   }
 

modules/libpref/init/StaticPrefList.yaml

@@ -4649,6 +4649,20 @@
   value: -1
   mirror: always
 
+# The time in number of frames that we estimate for a refresh driver
+# to be quiescent.
+- name: layout.idle_period.required_quiescent_frames
+  type: uint32_t
+  value: 2
+  mirror: always
+
+# The amount of time (milliseconds) needed between an idle period's
+# end and the start of the next tick to avoid jank.
+- name: layout.idle_period.time_limit
+  type: uint32_t
+  value: 1
+  mirror: always
+
 # Enable/disable interruptible reflow, which allows reflows to stop
 # before completion (and display the partial results) when user events
 # are pending.

modules/libpref/init/all.js

@@ -2985,14 +2985,6 @@ pref("layout.display-list.rebuild-frame-limit", 500);
 // pref to control whether layout warnings that are hit quite often are enabled
 pref("layout.spammy_warnings.enabled", false);
 
-// The number of frames times the frame rate is the time required to
-// pass without painting used to guess that we'll not paint again soon
-pref("layout.idle_period.required_quiescent_frames", 2);
-
-// The amount of time (milliseconds) needed between an idle period's
-// end and the start of the next tick to avoid jank.
-pref("layout.idle_period.time_limit", 1);
-
 // Pref to throttle offsreen animations
 pref("dom.animations.offscreen-throttling", true);