BackgroundImage incorrectly returns empty url() when created on-the-fly

Source/core/css/CSSImageValue.cpp

Index: Source/core/css/CSSImageValue.cpp
diff --git a/Source/core/css/CSSImageValue.cpp b/Source/core/css/CSSImageValue.cpp
index c4c6b7908d4f683764658f06c2e0ec6c29f2ac86..84b3ef63f15cd4e3aec873d5fbe75a5b6d5df766 100644
--- a/Source/core/css/CSSImageValue.cpp
+++ b/Source/core/css/CSSImageValue.cpp
@@ -108,7 +108,11 @@ bool CSSImageValue::equals(const CSSImageValue& other) const
 
 String CSSImageValue::customCSSText() const
 {
-    return "url(" + quoteCSSURLIfNeeded(m_absoluteURL) + ")";
+    if (m_absoluteURL.length())

[rune, 2015/09/08 23:57:28]

Gecko is using the relative URL. Looking at the CSSOM spec, it doesn't say
anything about serializing the absolute url. If the relative URL is available,
we should probably use that?

[nainar, 2015/09/09 00:30:30]

Done.

+        return "url(" + quoteCSSURLIfNeeded(m_absoluteURL) + ")";
+    if (m_relativeURL.length())
+        return "url(" + quoteCSSURLIfNeeded(m_relativeURL) + ")";
+    return "url()";
 }
 
 bool CSSImageValue::knownToBeOpaque(const LayoutObject* layoutObject) const