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..b5235fc8532f87410c7d7b37f09a9b1e61ad29cf 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++) {
@@ -711,8 +712,8 @@ String StylePropertySerializer::getLayeredShorthandValue(const StylePropertyShor
                 if (property == CSSPropertyBackgroundSize || property == CSSPropertyWebkitMaskSize) {
                     if (foundPositionYCSSProperty)

[Timothy Loh, 2016/02/08 05:29:28]

Maybe this should be:

if (foundPositionXCSSProperty || foundPositionYCSSProperty)
    " / "
else
    " 0% 0% / "

I think the current code will fail the position1 test if you changed
background-position to background-position-x. We might as well test that too.

                         layerResult.appendLiteral(" / ");
-                    else
-                        continue;
+                    else if (!foundPositionXCSSProperty)
+                        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)

[Timothy Loh, 2016/02/08 05:29:27]

might as well check for CSSPropertyWebkitMaskPositionX too for consistency

+                    foundPositionXCSSProperty = true;
                 if (property == CSSPropertyBackgroundPositionY || property == CSSPropertyWebkitMaskPositionY) {
                     foundPositionYCSSProperty = true;
                     // background-position is a special case. If only the first offset is specified,