Make List.remove return boolean.

sdk/lib/_collection_dev/list.dart

 // Copyright (c) 2013, 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.
 
 part of dart._collection.dev;
 
 /**
  * Mixin that throws on the length changing operations of [List].
  *
  * Intended to mix-in on top of [ListMixin] for fixed-length lists.
@@ skipping 17 matching lines @@
   void insertAll(int at, Iterable<E> iterable) {
     throw new UnsupportedError(
         "Cannot add to a fixed-length list");
   }
 
   void addAll(Iterable<E> iterable) {
     throw new UnsupportedError(
         "Cannot add to a fixed-length list");
   }
 
-  void remove(E element) {
+  bool remove(E element) {
     throw new UnsupportedError(
         "Cannot remove from a fixed-length list");
   }
 
   void removeAll(Iterable elements) {
     throw new UnsupportedError(
         "Cannot remove from a fixed-length list");
   }
 
   void retainAll(Iterable elements) {
@@ skipping 56 matching lines @@
         "Cannot change the length of an unmodifiable list");
   }
 
   void setAll(int at, Iterable<E> iterable) {
     throw new UnsupportedError(
         "Cannot modify an unmodifiable list");
   }
 
   void add(E value) {
     throw new UnsupportedError(
-        "Cannot add to an unmodifiable list");
+      "Cannot add to an unmodifiable list");
   }
 
   E insert(int index, E value) {
     throw new UnsupportedError(
         "Cannot add to an unmodifiable list");
   }
 
   void insertAll(int at, Iterable<E> iterable) {
     throw new UnsupportedError(
         "Cannot add to an unmodifiable list");
   }
 
   void addAll(Iterable<E> iterable) {
     throw new UnsupportedError(
         "Cannot add to an unmodifiable list");
   }
 
-  void remove(E element) {
+  bool remove(E element) {
     throw new UnsupportedError(
         "Cannot remove from an unmodifiable list");
   }
 
   void removeAll(Iterable elements) {
     throw new UnsupportedError(
         "Cannot remove from an unmodifiable list");
   }
 
   void retainAll(Iterable elements) {
@@ skipping 125 matching lines @@
 }
 
 class ReversedListIterable<E> extends ListIterable<E> {
   Iterable<E> _source;
   ReversedListIterable(this._source);
 
   int get length => _source.length;
 
   E elementAt(int index) => _source.elementAt(_source.length - 1 - index);
 }