Add "contains" method to Collection.

lib/compiler/implementation/lib/interceptors.dart

Index: lib/compiler/implementation/lib/interceptors.dart
diff --git a/lib/compiler/implementation/lib/interceptors.dart b/lib/compiler/implementation/lib/interceptors.dart
index 0c67b2224821e432ef2fffbc718309f3a75b46ab..2234648d5750b4d5ff768d4c87f2acaeedd2b0f7 100644
--- a/lib/compiler/implementation/lib/interceptors.dart
+++ b/lib/compiler/implementation/lib/interceptors.dart
@@ -516,10 +516,15 @@ concat(receiver, other) {
 }
 
 contains$1(receiver, other) {
-  if (receiver is !String) {
-    return UNINTERCEPTED(receiver.contains(other));
+  if (receiver is String) {
+    return contains$2(receiver, other, 0);
+  } else if (isJsArray(receiver)) {
+    for (int i = 0; i < receiver.length; i++) {
+      if (other == receiver[i]) return true;
+    }
+    return false;
   }
-  return contains$2(receiver, other, 0);
+  return UNINTERCEPTED(receiver.contains(other));
 }
 
 contains$2(receiver, other, startIndex) {