Support for --machine-problems, tests for PrettyErrorFormatter

compiler/java/com/google/dart/compiler/DefaultErrorFormatter.java

 // 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.
 
 package com.google.dart.compiler;
 
 import java.io.PrintStream;
 
 /**
  * An error formatter that simply prints the file name with the line and column
  * location.
  */
 public class DefaultErrorFormatter implements ErrorFormatter {
-  protected PrintStream outputStream = System.err;
-
-  public void setOutputStream(PrintStream outputStream) {
+  protected final PrintStream outputStream;
+  
+  public DefaultErrorFormatter(PrintStream outputStream) {
     this.outputStream = outputStream;
   }
 
   @Override
   public void format(DartCompilationError event) {
     outputStream.printf("%s:%d:%d: %s\n",
         (event.getSource() != null)
             ? event.getSource().getName() : "<unknown-source-file>",
         event.getLineNumber(),
         event.getColumnNumber(),
         event.getMessage());
   }
 }