Move isValid/isCurrentColor from Color to StyleColor

Source/web/mac/WebSubstringUtil.mm

Index: Source/web/mac/WebSubstringUtil.mm
diff --git a/Source/web/mac/WebSubstringUtil.mm b/Source/web/mac/WebSubstringUtil.mm
index 3574fb7defc7764e38120055a7c5cc8da744d154..89df63f7f990fe2a0d80999c7dc61b3241c93c31 100644
--- a/Source/web/mac/WebSubstringUtil.mm
+++ b/Source/web/mac/WebSubstringUtil.mm
@@ -91,11 +91,11 @@ NSAttributedString* WebSubstringUtil::attributedSubstringInRange(WebFrame* webFr
         [attrs setObject:font forKey:NSFontAttributeName];
 
         if (style->visitedDependentColor(CSSPropertyColor).alpha())
-            [attrs setObject:nsColor(style->visitedDependentColor(CSSPropertyColor)) forKey:NSForegroundColorAttributeName];
+            [attrs setObject:nsColor(renderer->resolveColor(CSSPropertyColor)) forKey:NSForegroundColorAttributeName];
         else
             [attrs removeObjectForKey:NSForegroundColorAttributeName];
         if (style->visitedDependentColor(CSSPropertyBackgroundColor).alpha())
-            [attrs setObject:nsColor(style->visitedDependentColor(CSSPropertyBackgroundColor)) forKey:NSBackgroundColorAttributeName];
+            [attrs setObject:nsColor(renderer->resolveColor(CSSPropertyBackgroundColor)) forKey:NSBackgroundColorAttributeName];
         else
             [attrs removeObjectForKey:NSBackgroundColorAttributeName];