Improve VM connection flow in Observatory

runtime/observatory/lib/src/app/page.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 app;
 
 final _allocationProfileRepository = new AllocationProfileRepository();
 final _breakpointRepository = new BreakpointRepository();
 final _classSampleProfileRepository = new ClassSampleProfileRepository();
 final _classRepository = new ClassRepository();
@@ skipping 134 matching lines @@
 
   void onInstall() {
     if (element == null) {
       element = container;
     }
     assert(element != null);
   }
 
   void _visit(Uri uri) {
     super._visit(uri);
+    if (app.vm == null) {
+      Logger.root.severe('VMPage has no VM');
+      // Reroute to vm-connect.
+      app.locationManager.go(Uris.vmConnect());
+      return;
+    }
     app.vm.reload().then((VM vm) {
       container.children = [
         new VMViewElement(vm, app.events, app.notifications,
                           _isolateRepository, _scriptRepository,
                           queue: app.queue)
       ];
     }).catchError((e, stack) {
       Logger.root.severe('VMPage visit error: $e');
       // Reroute to vm-connect.
-      app.locationManager.go(app.locationManager.makeLink('/vm-connect'));
+      app.locationManager.go(Uris.vmConnect());
     });
   }
 }
 
 class FlagsPage extends SimplePage {
   FlagsPage(app) : super('flags', 'flag-list', app);
 
   @override
   onInstall() {
     element = new FlagListElement(app.vm,
@@ skipping 621 matching lines @@
     element = new TimelinePageElement(app.vm, app.events, app.notifications,
                                       queue: app.queue);
   }
 
   void _visit(Uri uri) {
     assert(canVisit(uri));
   }
 
   bool canVisit(Uri uri) => uri.path == 'timeline';
 }