Introduce CSS_VALUE_TYPE_CASTS macro to cast CSSValue

Source/core/css/CSSValue.cpp

Index: Source/core/css/CSSValue.cpp
diff --git a/Source/core/css/CSSValue.cpp b/Source/core/css/CSSValue.cpp
index 1ffc0b146d81f3b432032050e79381fe4a84ff2e..702590d817b250ac81221a7fbe6f284706ef1efe 100644
--- a/Source/core/css/CSSValue.cpp
+++ b/Source/core/css/CSSValue.cpp
@@ -388,7 +388,7 @@ void CSSValue::destroy()
         delete toCSSPrimitiveValue(this);
         return;
     case ReflectClass:
-        delete static_cast<CSSReflectValue*>(this);
+        delete toCSSReflectValue(this);
         return;
     case ShadowClass:
         delete static_cast<ShadowValue*>(this);
@@ -415,7 +415,7 @@ void CSSValue::destroy()
         delete static_cast<CSSCalcValue*>(this);
         return;
     case ImageSetClass:
-        delete static_cast<CSSImageSetValue*>(this);
+        delete toCSSImageSetValue(this);
         return;
     case CSSFilterClass:
         delete static_cast<CSSFilterValue*>(this);