Preserve identical values for background-size and -webkit-mask-size.

Source/core/css/parser/CSSPropertyParser.cpp

Index: Source/core/css/parser/CSSPropertyParser.cpp
diff --git a/Source/core/css/parser/CSSPropertyParser.cpp b/Source/core/css/parser/CSSPropertyParser.cpp
index 7cc5f9a6fdb34e495578fb5337ecd9bd3036dbfc..96588feed050c025d2a5d82fdd01b987507b5275 100644
--- a/Source/core/css/parser/CSSPropertyParser.cpp
+++ b/Source/core/css/parser/CSSPropertyParser.cpp
@@ -2845,7 +2845,12 @@ PassRefPtrWillBeRawPtr<CSSValue> CSSPropertyParser::parseFillSize(CSSPropertyID
 
     if (!parsedValue2)
         return parsedValue1;
-    return createPrimitiveValuePair(parsedValue1.release(), parsedValue2.release());
+
+    // For backwards compatibility.

[ojan, 2014/04/24 01:12:38]

This comment seems somewhat lacking in context. Either it should explain more or
it shouldn't be there.

Also, won't this break with line 2843 above,i.e. if you just do background-size:
100%, won't that now serialize to background-size: 100% 100% ?

[andersr, 2014/04/24 11:05:42]

OK, I removed it.
No. Line 2843 applies to -webkit-background-size, not background-size.

For background-size, a value of '100%' means '100% auto', not '100% 100%'. For
-webkit-background-size, it *does* mean '100% 100%', which is why we use
DropIdenticalValues for this property.

+    Pair::IdenticalValuesPolicy policy = propId == CSSPropertyWebkitBackgroundSize ?
+        Pair::DropIdenticalValues : Pair::KeepIdenticalValues;
+
+    return createPrimitiveValuePair(parsedValue1.release(), parsedValue2.release(), policy);
 }
 
 bool CSSPropertyParser::parseFillProperty(CSSPropertyID propId, CSSPropertyID& propId1, CSSPropertyID& propId2,