Revert r154797: "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 996d7946293786456d2d92121ec7ade47b579826..f85491d9e53d2309644b7e4a8ff5ea752b021cb6 100644
--- a/Source/core/rendering/RenderMenuList.cpp
+++ b/Source/core/rendering/RenderMenuList.cpp
@@ -493,13 +493,9 @@ 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.alpha();
-    } else {
-        itemHasCustomBackgroundColor = false;
-    }
-
+    itemHasCustomBackgroundColor = backgroundColor.isValid() && backgroundColor.alpha();
     // If the item has an opaque background color, return that.
     if (!backgroundColor.hasAlpha()) {
         itemBackgroundColor = backgroundColor;