Add "contains" method to Collection.

runtime/lib/array.dart

Index: runtime/lib/array.dart
diff --git a/runtime/lib/array.dart b/runtime/lib/array.dart
index 75a674f745f8a6eef678df80a9694b6a8a8fa590..ef5aef7fbeb581a137efd39b15e010562f5edb80 100644
--- a/runtime/lib/array.dart
+++ b/runtime/lib/array.dart
@@ -59,9 +59,9 @@ class _ObjectArray<E> implements List<E> {
     return list;
   }
 
-  /**
-   * Collection interface.
-   */
+  // Collection interface.
+
+  bool contains(E element) => Collections.contains(this, element);
 
   void forEach(f(E element)) {
     Collections.forEach(this, f);
@@ -201,9 +201,9 @@ class _ImmutableArray<E> implements List<E> {
     return list;
   }
 
-  /**
-   * Collection interface.
-   */
+  // Collection interface.
+
+  bool contains(E element) => Collections.contains(this, element);
 
   void forEach(f(E element)) {
     Collections.forEach(this, f);