Split out String, URI and CustomIdent from CSSPrimitiveValue

Source/core/css/resolver/StyleBuilderConverter.h

Index: Source/core/css/resolver/StyleBuilderConverter.h
diff --git a/Source/core/css/resolver/StyleBuilderConverter.h b/Source/core/css/resolver/StyleBuilderConverter.h
index b6bfd25be0f9a706d9b24689605f0da1f35e10a0..7020d4c53c4da3cb0e0cbefaecc6a8fc2ae399c7 100644
--- a/Source/core/css/resolver/StyleBuilderConverter.h
+++ b/Source/core/css/resolver/StyleBuilderConverter.h
@@ -27,6 +27,7 @@
 #ifndef StyleBuilderConverter_h
 #define StyleBuilderConverter_h
 
+#include "core/css/CSSStringValue.h"
 #include "core/css/CSSValue.h"
 #include "core/css/CSSValueList.h"
 #include "core/css/resolver/StyleResolverState.h"
@@ -154,11 +155,12 @@ T StyleBuilderConverter::convertLineWidth(StyleResolverState& state, CSSValue* v
 template <CSSValueID IdForNone>
 AtomicString StyleBuilderConverter::convertString(StyleResolverState&, CSSValue* value)
 {
-    CSSPrimitiveValue* primitiveValue = toCSSPrimitiveValue(value);
-    if (primitiveValue->getValueID() == IdForNone)
+    if (value->isPrimitiveValue() && toCSSPrimitiveValue(value)->getValueID() == IdForNone)
         return nullAtom;
-    ASSERT(primitiveValue->isString());
-    return AtomicString(primitiveValue->getStringValue());
+    if (value->isStringValue() && toCSSStringValue(value)->serializationType() == CSSStringValue::SerializeAsString)
+        return AtomicString(toCSSStringValue(value)->getStringValue());
+    ASSERT_NOT_REACHED();
+    return nullAtom;
 }
 
 } // namespace blink