Move exception support to its own library

pkg/analysis_server/lib/src/status/tree_writer.dart

 // Copyright (c) 2015, 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.
 
 library analysis_server.src.status.tree_writer;
 
 import 'dart:convert';
 
+import 'package:analyzer/exception/exception.dart';
 import 'package:analyzer/src/dart/element/element.dart';
 import 'package:analyzer/src/generated/constant.dart';
-import 'package:analyzer/src/generated/java_engine.dart';
 import 'package:analyzer/src/generated/source.dart';
 
 /**
  * Utility methods that can be mixed in to classes that produce an HTML
  * representation of a tree structure.
  */
 abstract class TreeWriter {
   /**
    * The buffer on which the HTML is to be written.
    */
@@ skipping 94 matching lines @@
       if (valueString == null) {
         buffer.write('<span style="color: #FF0000">');
         buffer.write(HTML_ESCAPE.convert(value.runtimeType.toString()));
         buffer.write('</span>');
       } else {
         buffer.write(HTML_ESCAPE.convert(valueString));
       }
     }
   }
 }