Mark DOMStringList.contains() as deprecated, add console warning.

Source/core/frame/UseCounter.cpp

 /*
  * Copyright (C) 2012 Google, Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 910 matching lines @@
 
     case CSSSelectorPseudoShadow:
         return "::shadow pseudo-element is deprecated. See https://www.chromestatus.com/features/6750456638341120 for more details.";
 
     case PrefixedMouseEventMovementX:
         return replacedBy("webkitMovementX", "movementX");
 
     case PrefixedMouseEventMovementY:
         return replacedBy("webkitMovementY", "movementY");
 
+    case DOMStringListContains:
+        return "'DOMStringList.contains()' is deprecated, and will be removed.";
+
+    case DOMStringListItem:
+        return "'DOMStringList.item(n)' is deprecated, and will be removed. Please use indexing instead, e.g.: list[n]";
+
     // Features that aren't deprecated don't have a deprecation message.
     default:
         return String();
     }
 }
 
 void UseCounter::count(CSSParserContext context, CSSPropertyID feature)
 {
     ASSERT(feature >= firstCSSProperty);
     ASSERT(feature <= lastUnresolvedCSSProperty);
@@ skipping 27 matching lines @@
 UseCounter* UseCounter::getFrom(const StyleSheetContents* sheetContents)
 {
     // FIXME: We may want to handle stylesheets that have multiple owners
     //        http://crbug.com/242125
     if (sheetContents && sheetContents->hasSingleOwnerNode())
         return getFrom(sheetContents->singleOwnerDocument());
     return 0;
 }
 
 } // namespace blink