Make List.remove return boolean.

runtime/lib/growable_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.
 
 class _GrowableObjectArray<T> implements List<T> {
   factory _GrowableObjectArray._uninstantiable() {
     throw new UnsupportedError(
         "GrowableObjectArray can only be allocated by the VM");
   }
 
@@ skipping 25 matching lines @@
     int newLength = this.length - 1;
     Arrays.copy(this,
                 index + 1,
                 this,
                 index,
                 newLength - index);
     this.length = newLength;
     return result;
   }
 
-  void remove(Object element) {
+  bool remove(Object element) {
     for (int i = 0; i < this.length; i++) {
       if (this[i] == element) {
         removeAt(i);
-        return;
+        return true;
       }
     }
+    return false;
   }
 
   void insertAll(int index, Iterable<T> iterable) {
     if (index < 0 || index > length) {
       throw new RangeError.range(index, 0, length);
     }
     // TODO(floitsch): we can probably detect more cases.
     if (iterable is! List && iterable is! Set && iterable is! SubListIterable) {
       iterable = iterable.toList();
     }
@@ skipping 286 matching lines @@
   }
 
   Set<T> toSet() {
     return new Set<T>.from(this);
   }
 
   Map<int, T> asMap() {
     return IterableMixinWorkaround.asMapList(this);
   }
 }