Improve script display in the observatory.

runtime/bin/vmservice/client/lib/src/service/object.dart

 // Copyright (c) 2014, 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.
 
 part of service;
 
 /// A [ServiceObject] is an object known to the VM service and is tied
 /// to an owning [Isolate].
 abstract class ServiceObject extends Observable {
   static int LexicalSortName(ServiceObject o1, ServiceObject o2) {
@@ skipping 1227 matching lines @@
 
   Script._empty(ServiceObjectOwner owner) : super._empty(owner);
 
   ScriptLine getLine(int line) {
     assert(line >= 1);
     return lines[line - 1];
   }
 
   /// This function maps a token position to a line number.
   int tokenToLine(int token) => _tokenToLine[token];
-  Map _tokenToLine;
+  Map _tokenToLine = {};
 
   /// This function maps a token position to a column number.
   int tokenToCol(int token) => _tokenToCol[token];
-  Map _tokenToCol;
+  Map _tokenToCol = {};
 
   void _update(ObservableMap map, bool mapIsRef) {
     kind = map['kind'];
     _url = map['name'];
     _shortUrl = _url.substring(_url.lastIndexOf('/') + 1);
     name = _shortUrl;
     vmName = _url;
     _processSource(map['source']);
     _parseTokenPosTable(map['tokenPosTable']);
   }
 
   void _parseTokenPosTable(List<List<int>> table) {
     if (table == null) {
       return;
     }
-    _tokenToLine = {};
-    _tokenToCol = {};
+    _tokenToLine.clear();
+    _tokenToCol.clear();
     firstTokenPos = null;
     lastTokenPos = null;
     for (var line in table) {
       // Each entry begins with a line number...
       var lineNumber = line[0];
       for (var pos = 1; pos < line.length; pos += 2) {
         // ...and is followed by (token offset, col number) pairs.
         var tokenOffset = line[pos];
         var colNumber = line[pos+1];
         if (firstTokenPos == null) {
@@ skipping 636 matching lines @@
     var v = list[i];
     if ((v is ObservableMap) && _isServiceMap(v)) {
       list[i] = owner.getFromMap(v);
     } else if (v is ObservableList) {
       _upgradeObservableList(v, owner);
     } else if (v is ObservableMap) {
       _upgradeObservableMap(v, owner);
     }
   }
 }