Move isValid/isCurrentColor from Color to StyleColor

Source/core/rendering/RenderMenuList.cpp

Index: Source/core/rendering/RenderMenuList.cpp
diff --git a/Source/core/rendering/RenderMenuList.cpp b/Source/core/rendering/RenderMenuList.cpp
index b984d7ea5e151c3ea58d8dec7715dca7b5a28724..241185f9ea83bdec168e0d4980d91edb2a481847 100644
--- a/Source/core/rendering/RenderMenuList.cpp
+++ b/Source/core/rendering/RenderMenuList.cpp
@@ -491,9 +491,13 @@ void RenderMenuList::getItemBackgroundColor(unsigned listIndex, Color& itemBackg
     HTMLElement* element = listItems[listIndex];
 
     Color backgroundColor;
-    if (element->renderStyle())
+    if (element->renderStyle()) {
         backgroundColor = resolveColor(element->renderStyle(), CSSPropertyBackgroundColor);
-    itemHasCustomBackgroundColor = backgroundColor.isValid() && backgroundColor.alpha();
+        itemHasCustomBackgroundColor = backgroundColor.alpha();
+    } else {
+        itemHasCustomBackgroundColor = false;
+    }
+
     // If the item has an opaque background color, return that.
     if (!backgroundColor.hasAlpha()) {
         itemBackgroundColor = backgroundColor;