Reorder one line to prevent possible race.

tools/ddbg.dart

 // Copyright (c) 2012, 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.
 
 // Simple interactive debugger shell that connects to the Dart VM's debugger
 // connection port.
 
 import "dart:convert";
 import "dart:io";
 import "dart:async";
@@ skipping 948 matching lines @@
 }
 
 
 Future<TargetScript> getTargetScript(Map location) {
   var isolate = targetIsolates[currentIsolate.id];
   var url = location['url'];
   var script = isolate.scripts[url];
   if (script != null) {
     return new Future.value(script);
   }
+  script = new TargetScript();
 
   // Ask the vm for the source and line number table.
   var sourceCmd = {
     "id": seqNum++,
     "command":  "getScriptSource",
     "params": { "isolateId": currentIsolate.id,
                 "libraryId": location['libraryId'],
                 "url": url } };
 
   var lineNumberCmd = {
@@ skipping 11 matching lines @@
       script.lineToSource = [''];
       script.lineToSource.addAll(script.source.split('\n'));
     });
 
   // Send the line numbers command
   var lineNumberResponse = sendCmd(lineNumberCmd).then((response) {
       Map result = response["result"];
       script.tokenToLine = parseLineNumberTable(result['lines']);
     });
 
-  script = new TargetScript();
   return Future.wait([sourceResponse, lineNumberResponse]).then((_) {
       // When both commands complete, cache the result.
       isolate.scripts[url] = script;
       return script;
     });
 }
 
 
 Future printLocation(String label, Map location) {
   // Figure out the line number.
@@ skipping 398 matching lines @@
       handleUncaughtError: debuggerError));
 
   zone.run(() {
       parseArgs(args);
       cmdo = new Commando(completer: debuggerCommandCompleter);
       cmdSubscription = cmdo.commands.listen(processCommand,
                                              onError: processError,
                                              onDone: processDone);
     });
 }