Change IllegalArgumentException to ArgumentError.

lib/coreimpl/future_implementation.dart

 // Copyright 2012 Google Inc. All Rights Reserved.
 // Dart core library.
 
 class FutureImpl<T> implements Future<T> {
 
   bool _isComplete = false;
 
   /**
    * Value that was provided to this Future by the Completer
    */
@@ skipping 141 matching lines @@
     if (_isComplete) {
       throw new FutureAlreadyCompleteException();
     }
     _value = value;
     _complete();
   }
 
   void _setException(Object exception, Object stackTrace) {
     if (exception === null) {
       // null is not a legal value for the exception of a Future.
-      throw new IllegalArgumentException(null);
+      throw new ArgumentError(null);
     }
     if (_isComplete) {
       throw new FutureAlreadyCompleteException();
     }
     _exception = exception;
     _stackTrace = stackTrace;
     _complete();
   }
 
   Future transform(Function transformation) {
@@ skipping 88 matching lines @@
   }
 
   void complete(T value) {
     _futureImpl._setValue(value);
   }
 
   void completeException(Object exception, [Object stackTrace]) {
     _futureImpl._setException(exception, stackTrace);
   }
 }