Bug 904263 - check pref settings more efficiently. r=dbaron

layout/style/Declaration.cpp

@@ -568,8 +568,9 @@ Declaration::GetValue(nsCSSProperty aProperty, nsAString& aValue) const
 
       // if font features are not enabled, pointers for fontVariant
       // values above may be null since the shorthand check ignores them
+      // font-variant-alternates enabled ==> layout.css.font-features.enabled is true
       bool fontFeaturesEnabled =
-        mozilla::Preferences::GetBool("layout.css.font-features.enabled");
+        nsCSSProps::IsEnabled(eCSSProperty_font_variant_alternates);
 
       if (systemFont &&
           systemFont->GetUnit() != eCSSUnit_None &&

layout/style/nsCSSParser.cpp

@@ -8515,8 +8515,9 @@ CSSParserImpl::ParseFont()
     eCSSProperty_font_weight
   };
 
+  // font-variant-alternates enabled ==> layout.css.font-features.enabled is true
   bool featuresEnabled =
-    mozilla::Preferences::GetBool("layout.css.font-features.enabled");
+    nsCSSProps::IsEnabled(eCSSProperty_font_variant_alternates);
   nsCSSValue  family;
   if (ParseVariant(family, VARIANT_HK, nsCSSProps::kFontKTable)) {
     if (ExpectEndProperty()) {

layout/style/nsCSSProps.cpp

@@ -412,9 +412,12 @@ nsCSSProps::LookupFontDesc(const nsAString& aFontDesc)
   NS_ABORT_IF_FALSE(gFontDescTable, "no lookup table, needs addref");
   nsCSSFontDesc which = nsCSSFontDesc(gFontDescTable->Lookup(aFontDesc));
 
+  // font-variant-alternates enabled ==> layout.css.font-features.enabled is true
+  bool fontFeaturesEnabled =
+    nsCSSProps::IsEnabled(eCSSProperty_font_variant_alternates);
+
   // check for unprefixed font-feature-settings/font-language-override
-  if (which == eCSSFontDesc_UNKNOWN &&
-      mozilla::Preferences::GetBool("layout.css.font-features.enabled")) {
+  if (which == eCSSFontDesc_UNKNOWN && fontFeaturesEnabled) {
     nsAutoString prefixedProp;
     prefixedProp.AppendLiteral("-moz-");
     prefixedProp.Append(aFontDesc);

layout/style/nsCSSRules.h

@@ -335,7 +335,11 @@ public:
 
   static bool PrefEnabled()
   {
-    return mozilla::Preferences::GetBool("layout.css.font-features.enabled");
+    // font-variant-alternates enabled ==> layout.css.font-features.enabled is true
+    bool fontFeaturesEnabled =
+      nsCSSProps::IsEnabled(eCSSProperty_font_variant_alternates);
+
+    return fontFeaturesEnabled;
   }
 
 protected: