Make List.remove return boolean.

runtime/lib/array.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 
 // TODO(srdjan): Use shared array implementation.
 class _ObjectArray<E> implements List<E> {
 
   factory _ObjectArray(length) native "ObjectArray_allocate";
 
@@ skipping 25 matching lines @@
 
   void setAll(int index, Iterable<E> iterable) {
     IterableMixinWorkaround.setAllList(this, index, iterable);
   }
 
   E removeAt(int index) {
     throw new UnsupportedError(
         "Cannot remove element of a non-extendable array");
   }
 
-  void remove(Object element) {
+  bool remove(Object element) {
     throw new UnsupportedError(
         "Cannot remove element of a non-extendable array");
   }
 
   void removeWhere(bool test(E element)) {
     throw new UnsupportedError(
         "Cannot remove element of a non-extendable array");
   }
 
   void retainWhere(bool test(E element)) {
@@ skipping 246 matching lines @@
   void setAll(int index, Iterable<E> iterable) {
     throw new UnsupportedError(
         "Cannot modify an immutable array");
   }
 
   E removeAt(int index) {
     throw new UnsupportedError(
         "Cannot modify an immutable array");
   }
 
-  void remove(Object element) {
+  bool remove(Object element) {
     throw new UnsupportedError(
         "Cannot modify an immutable array");
   }
 
   void removeWhere(bool test(E element)) {
     throw new UnsupportedError(
         "Cannot modify an immutable array");
   }
 
   void retainWhere(bool test(E element)) {
@@ skipping 219 matching lines @@
     }
     _position = _length;
     _current = null;
     return false;
   }
 
   E get current {
     return _current;
   }
 }