Bug 773296 - Part 14: Add an nsCSSProps::IsInherited function. r=dbaron

Add a helper function to nsCSSProps to look up whether a given
nsCSSProperty lives in a style struct for inherited properties.

layout/style/nsCSSProps.cpp

@@ -349,6 +349,15 @@ nsCSSProps::ReleaseTable(void)
 // Length of the "var-" custom property name prefix.
 #define VAR_PREFIX_LENGTH 4
 
+/* static */ bool
+nsCSSProps::IsInherited(nsCSSProperty aProperty)
+{
+  MOZ_ASSERT(!IsShorthand(aProperty));
+
+  nsStyleStructID sid = kSIDTable[aProperty];
+  return nsCachedStyleData::IsInherited(sid);
+}
+
 /* static */ bool
 nsCSSProps::IsCustomPropertyName(const nsACString& aProperty)
 {

layout/style/nsCSSProps.h

@@ -270,6 +270,9 @@ public:
     return (aProperty >= eCSSProperty_COUNT_no_shorthands);
   }
 
+  // Must be given a longhand property.
+  static bool IsInherited(nsCSSProperty aProperty);
+
   // Same but for @font-face descriptors
   static nsCSSFontDesc LookupFontDesc(const nsAString& aProperty);
   static nsCSSFontDesc LookupFontDesc(const nsACString& aProperty);