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 f1dd55d2836847fe849654b6f14e306490af1094..393370b25e947712031b4877f07f550c725f2244 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/CSSStringValueBase.h"
 #include "core/css/CSSValue.h"
 #include "core/css/CSSValueList.h"
 #include "core/css/resolver/StyleResolverState.h"
@@ -153,11 +154,9 @@ 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());
+    return AtomicString(toCSSStringValue(value)->value());
 }
 
 } // namespace blink