Add pause/resume for isolates in vmservice/observatory.

runtime/bin/vmservice/client/lib/src/elements/script_inset.dart

 // Copyright (c) 2013, 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 script_inset_element;
 
 import 'observatory_element.dart';
 import 'package:observatory/service.dart';
 import 'package:polymer/polymer.dart';
 
@@ skipping 46 matching lines @@
       script.load().then((_) {
           if (script.loaded) {
             _updateProperties();
           }
         });
       return;
     }
     notifyPropertyChange(#lines, 0, 1);
     lines.clear();
     var startLineNumber = script.tokenToLine(pos);
-    if (endPos == null) {
-      lines.add(script.lines[startLineNumber - 1]);
-    } else {
-      var endLineNumber = script.tokenToLine(endPos);
-      assert(endLineNumber != null);
-      for (var i = startLineNumber; i <= endLineNumber; i++) {
-        lines.add(script.lines[i - 1]);
+    if (startLineNumber != null) {
+      if (endPos == null) {  
+        lines.add(script.lines[startLineNumber - 1]);
+      } else {
+        var endLineNumber = script.tokenToLine(endPos);
+        assert(endLineNumber != null);
+        for (var i = startLineNumber; i <= endLineNumber; i++) {
+          lines.add(script.lines[i - 1]);
+        }
       }
     }
   }
 
   ScriptInsetElement.created() : super.created();
 }