Add toSVGColor|Paint() to cleanup static_cast<>, and use it

Source/bindings/v8/custom/V8CSSValueCustom.cpp

Index: Source/bindings/v8/custom/V8CSSValueCustom.cpp
diff --git a/Source/bindings/v8/custom/V8CSSValueCustom.cpp b/Source/bindings/v8/custom/V8CSSValueCustom.cpp
index 77f7c6fd6b58f8faa0747bc6b134d15b794b774e..3db5c35477c627679d7955cac51919145868d19a 100644
--- a/Source/bindings/v8/custom/V8CSSValueCustom.cpp
+++ b/Source/bindings/v8/custom/V8CSSValueCustom.cpp
@@ -56,9 +56,9 @@ v8::Handle<v8::Object> wrap(CSSValue* impl, v8::Handle<v8::Object> creationConte
     if (impl->isPrimitiveValue())
         return wrap(toCSSPrimitiveValue(impl), creationContext, isolate);
     if (impl->isSVGPaint())
-        return wrap(static_cast<SVGPaint*>(impl), creationContext, isolate);
+        return wrap(toSVGPaint(impl), creationContext, isolate);
     if (impl->isSVGColor())
-        return wrap(static_cast<SVGColor*>(impl), creationContext, isolate);
+        return wrap(toSVGColor(impl), creationContext, isolate);
     return V8CSSValue::createWrapper(impl, creationContext, isolate);
 }