Bug 1573268 - Convert font.size.systemFontScale to static pref. r=njn

Converts font.size.systemFontScale to a static pref. Removes the function in nsLayoutUtils and does the float division directly in PresShell.

Differential Revision: https://phabricator.services.mozilla.com/D41824

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

layout/base/PresShell.cpp

@@ -10751,7 +10751,8 @@ nsSize PresShell::GetLayoutViewportSize() const {
 void PresShell::RecomputeFontSizeInflationEnabled() {
   mFontSizeInflationEnabled = DetermineFontSizeInflationState();
 
-  float fontScale = nsLayoutUtils::SystemFontScale();
+  // Divide by 100 to convert the pref from a percentage to a fraction.
+  float fontScale = StaticPrefs::font_size_systemFontScale() / 100.0f;
   if (fontScale == 0.0f) {
     return;
   }

layout/base/nsLayoutUtils.cpp

@@ -183,8 +183,6 @@ bool nsLayoutUtils::gPreventAssertInCompareTreePosition = false;
 typedef ScrollableLayerGuid::ViewID ViewID;
 typedef nsStyleTransformMatrix::TransformReferenceBox TransformReferenceBox;
 
-/* static */
-uint32_t nsLayoutUtils::sSystemFontScale;
 /* static */
 uint32_t nsLayoutUtils::sZoomMaxPercent;
 /* static */
@@ -7973,8 +7971,6 @@ size_t nsLayoutUtils::SizeOfTextRunsForFrames(nsIFrame* aFrame,
 
 /* static */
 void nsLayoutUtils::Initialize() {
-  Preferences::AddUintVarCache(&sSystemFontScale, "font.size.systemFontScale",
-                               100);
   Preferences::AddUintVarCache(&sZoomMaxPercent, "zoom.maxPercent", 300);
   Preferences::AddUintVarCache(&sZoomMinPercent, "zoom.minPercent", 30);
   Preferences::AddBoolVarCache(&sInvalidationDebuggingIsEnabled,

layout/base/nsLayoutUtils.h

@@ -2445,12 +2445,6 @@ class nsLayoutUtils {
 
   static bool FontSizeInflationEnabled(nsPresContext* aPresContext);
 
-  /**
-   * See comment above "font.size.systemFontScale" in
-   * modules/libpref/init/all.js.
-   */
-  static float SystemFontScale() { return sSystemFontScale / 100.0f; }
-
   static float MaxZoom() { return sZoomMaxPercent / 100.0f; }
 
   static float MinZoom() { return sZoomMinPercent / 100.0f; }
@@ -3009,7 +3003,6 @@ class nsLayoutUtils {
       const nsIFrame* aFrame);
 
  private:
-  static uint32_t sSystemFontScale;
   static uint32_t sZoomMaxPercent;
   static uint32_t sZoomMinPercent;
   static bool sInvalidationDebuggingIsEnabled;

modules/libpref/init/StaticPrefList.yaml

@@ -2639,6 +2639,18 @@
   value: 0
   mirror: always
 
+# This setting corresponds to a global text zoom setting affecting
+# all content that is not already subject to font size inflation.
+# It is interpreted as a percentage value that is applied on top
+# of the document's current text zoom setting.
+#
+# The resulting total zoom factor (text zoom * system font scale)
+# will be limited by zoom.minPercent and maxPercent.
+- name: font.size.systemFontScale
+  type: uint32_t
+  value: 100
+  mirror: always
+
 #---------------------------------------------------------------------------
 # Prefs starting with "full-screen-api."
 #---------------------------------------------------------------------------

modules/libpref/init/all.js

@@ -3357,17 +3357,6 @@ pref("font.minimum-size.x-math", 0);
 pref("font.size.variable.x-math", 16);
 pref("font.size.monospace.x-math", 13);
 
-/**
- * This setting corresponds to a global text zoom setting affecting
- * all content that is not already subject to font size inflation.
- * It is interpreted as a percentage value that is applied on top
- * of the document's current text zoom setting.
- *
- * The resulting total zoom factor (text zoom * system font scale)
- * will be limited by zoom.minPercent and maxPercent.
- */
-pref("font.size.systemFontScale", 100);
-
 /*
  * When enabled, the touch.radius and mouse.radius prefs allow events to be dispatched
  * to nearby elements that are sensitive to the event. See PositionedEventTargeting.cpp.