Support for --machine-problems, tests for PrettyErrorFormatter

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

Index: compiler/java/com/google/dart/compiler/DefaultErrorFormatter.java
diff --git a/compiler/java/com/google/dart/compiler/DefaultErrorFormatter.java b/compiler/java/com/google/dart/compiler/DefaultErrorFormatter.java
index df0cfe545d1e0137716d7ca7b3bd33dbe8e866a8..898cb322e9b0f4a40e9447932747680394fc43de 100644
--- a/compiler/java/com/google/dart/compiler/DefaultErrorFormatter.java
+++ b/compiler/java/com/google/dart/compiler/DefaultErrorFormatter.java
@@ -11,9 +11,9 @@ import java.io.PrintStream;
  * 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;
   }