Fix background-size serializing

third_party/WebKit/Source/core/css/StylePropertySerializer.cpp

Index: third_party/WebKit/Source/core/css/StylePropertySerializer.cpp
diff --git a/third_party/WebKit/Source/core/css/StylePropertySerializer.cpp b/third_party/WebKit/Source/core/css/StylePropertySerializer.cpp
index bac63e9869bfdf8c31e7585bef0aa8b4e66d4652..d9af51efb45727fe9c71177107e023ab23c74c8c 100644
--- a/third_party/WebKit/Source/core/css/StylePropertySerializer.cpp
+++ b/third_party/WebKit/Source/core/css/StylePropertySerializer.cpp
@@ -659,6 +659,7 @@ String StylePropertySerializer::getLayeredShorthandValue(const StylePropertyShor
         bool useRepeatXShorthand = false;
         bool useRepeatYShorthand = false;
         bool useSingleWordShorthand = false;
+        bool foundPositionXCSSProperty = false;
         bool foundPositionYCSSProperty = false;
 
         for (unsigned propertyIndex = 0; propertyIndex < size; propertyIndex++) {
@@ -709,10 +710,10 @@ String StylePropertySerializer::getLayeredShorthandValue(const StylePropertyShor
 
             if (!(value->isInitialValue() && toCSSInitialValue(value)->isImplicit())) {
                 if (property == CSSPropertyBackgroundSize || property == CSSPropertyWebkitMaskSize) {
-                    if (foundPositionYCSSProperty)
+                    if (foundPositionYCSSProperty || foundPositionXCSSProperty)
                         layerResult.appendLiteral(" / ");
                     else
-                        continue;
+                        layerResult.appendLiteral(" 0% 0% / ");
                 } else if (!layerResult.isEmpty()) {
                     // Do this second to avoid ending up with an extra space in the output if we hit the continue above.
                     layerResult.append(' ');
@@ -729,6 +730,8 @@ String StylePropertySerializer::getLayeredShorthandValue(const StylePropertyShor
                         useSingleWordShorthand = false;
                     layerResult.append(value->cssText());
                 }
+                if (property == CSSPropertyBackgroundPositionX || property == CSSPropertyWebkitMaskPositionX)
+                    foundPositionXCSSProperty = true;
                 if (property == CSSPropertyBackgroundPositionY || property == CSSPropertyWebkitMaskPositionY) {
                     foundPositionYCSSProperty = true;
                     // background-position is a special case. If only the first offset is specified,