Generated code README and headers.

editor/util/plugins/com.google.dart.java2dart/src/com/google/dart/java2dart/engine/MainEngine.java

Index: editor/util/plugins/com.google.dart.java2dart/src/com/google/dart/java2dart/engine/MainEngine.java
===================================================================
--- editor/util/plugins/com.google.dart.java2dart/src/com/google/dart/java2dart/engine/MainEngine.java	(revision 17788)
+++ editor/util/plugins/com.google.dart.java2dart/src/com/google/dart/java2dart/engine/MainEngine.java	(working copy)
@@ -50,6 +50,9 @@
       PropertySemanticProcessor.INSTANCE,
       EngineSemanticProcessor.INSTANCE);
 
+  private static final String HEADER = "// This code was auto-generated, is not intended to be edited, and is subject to\n"
+      + "// significant change. Please see the README file for more information.\n\n";
+
   public static void main(String[] args) throws Exception {
     if (args.length == 0) {
       System.out.println("Usage: java2dart <target-folder>");
@@ -236,6 +239,7 @@
    */
   private static String getFormattedSource(ASTNode node) {
     PrintStringWriter writer = new PrintStringWriter();
+    writer.append(HEADER);
     node.accept(new ToFormattedSourceVisitor(writer));
     return writer.toString();
   }