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

Source/core/dom/DOMStringList.idl

Index: Source/core/dom/DOMStringList.idl
diff --git a/Source/core/dom/DOMStringList.idl b/Source/core/dom/DOMStringList.idl
index ca27f1d5ac3838aa8540314185c5e39ab688922c..1bd16c9f915389c693385004ae20250c135644cd 100644
--- a/Source/core/dom/DOMStringList.idl
+++ b/Source/core/dom/DOMStringList.idl
@@ -30,6 +30,8 @@
     WillBeGarbageCollected,
 ] interface DOMStringList {
     readonly attribute unsigned long length;
-    getter DOMString? item(unsigned long index);
-    [MeasureAs=DOMStringListContains] boolean contains(DOMString string);
+    [DeprecateAs=DOMStringListItem] DOMString? item(unsigned long index);
+    getter DOMString? (unsigned long index);
+    // FIXME: If Array.prototype.includes is added, add includes() and update deprecation message.

[philipj_slow, 2015/03/06 03:03:49]

I don't think it's a given that we'll want to add DOMStringList.includes or that
doing so would help the transition, so... remove this FIXME, wait and see?

[jsbell, 2015/03/06 17:19:20]

Done.

+    [DeprecateAs=DOMStringListContains] boolean contains(DOMString string);
 };