Support tab completion of line:col in the debugger.

runtime/observatory/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;
 
 /// Helper function for canceling a Future<StreamSubscription>.
 Future cancelFutureSubscription(
     Future<StreamSubscription> subscriptionFuture) async {
   if (subscriptionFuture != null) {
@@ skipping 1488 matching lines @@
       if (bpt.resolved && script.loaded) {
         SourceLocation loc = bpt.location;
         if (script.tokenToLine(loc.tokenPos) != line) {
           script.getLine(line).possibleBpt = false;
         }
       }
       return bpt;
     } on ServerRpcException catch(e) {
       if (e.code == ServerRpcException.kCannotAddBreakpoint) {
         // Unable to set a breakpoint at the desired line.
-        script.getLine(line).possibleBpt = false;
+        if (script.loaded) {
+          script.getLine(line).possibleBpt = false;
+        }
       }
       rethrow;
     }
   }
 
   Future<ServiceObject> addBreakpointByScriptUri(
       String uri, int line, [int col]) {
     Map params = {
       'scriptUri': uri,
       'line': line.toString(),
@@ skipping 2412 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);
     }
   }
 }