Fix process test and implementation after change to setter for registering event handler.

tests/standalone/src/ProcessExitNegativeTest.dart

 // Copyright (c) 2011, 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.
 //
 // Process test program to test that compilation errors in the process
 // exit handler is reported correctly.
 
 void main() {
   Process p = new Process("true", []);
-  p.setExitHandler(
-    (int s) {
-      print(a.toString());  // Should cause a compilation error here.
-      p.close();
-    }
-  );
+  p.exitHandler = (int s) {
+    print(a.toString());  // Should cause a compilation error here.
+    p.close();
+  };
   p.start();
 }