When attempting to navigate to a page for an isolate that doesn't exist, offer to

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;
 
+class IsolateNotFound implements Exception {
+  String isolateId;
+  IsolateNotFound(this.isolateId);
+  String toString() => "IsolateNotFound: $isolateId";
+}
+
 /// A [Page] controls the user interface of Observatory. At any given time
 /// one page will be the current page. Pages are registered at startup.
 /// When the user navigates within the application, each page is asked if it
 /// can handle the current location, the first page to say yes, wins.
 abstract class Page extends Observable {
   final ObservatoryApplication app;
   final ObservableMap<String, String> internalArguments =
       new ObservableMap<String, String>();
   @observable ObservatoryElement element;
 
@@ skipping 35 matching lines @@
       element = new Element.tag(elementTagName);
     }
   }
 
   void _visit(Uri uri) {
     assert(uri != null);
     assert(canVisit(uri));
   }
 
   Future<Isolate> getIsolate(Uri uri) {
-    return app.vm.getIsolate(uri.queryParameters['isolateId'])
-      .catchError((e, stack) {
-        Logger.root.severe('$path visit error: $e\n$stack');
-        return e;
-      });
+    var isolateId = uri.queryParameters['isolateId'];
+    return app.vm.getIsolate(isolateId).then((isolate) {

[rmacnak, 2015/04/23 18:32:19]

Probably push this into the service library.

[turnidge, 2015/05/01 17:23:55]

I'm working on this currently in another CL.

+      if (isolate == null) {
+        throw new IsolateNotFound(isolateId);
+      }
+      return isolate;
+    });
   }
 
   bool canVisit(Uri uri) => uri.path == path;
 }
 
 /// Error page for unrecognized paths.
 class ErrorPage extends Page {
   ErrorPage(app) : super(app);
 
   void onInstall() {
@@ skipping 208 matching lines @@
       element = new Element.tag('vm-connect');
     }
     assert(element != null);
   }
 
   void _visit(Uri uri) {
     assert(element != null);
     assert(canVisit(uri));
   }
 
-  // TODO(turnidge): Update this to not have the trailing slash.
-  bool canVisit(Uri uri) => uri.path.startsWith('vm-connect/');
+  bool canVisit(Uri uri) => uri.path.startsWith('vm-connect');
+}
+
+class IsolateReconnectPage extends Page {
+  IsolateReconnectPage(app) : super(app);
+
+  void onInstall() {
+    if (element == null) {
+      element = new Element.tag('isolate-reconnect');
+    }
+    assert(element != null);
+  }
+
+  void _visit(Uri uri) {
+    app.vm.reload();
+    assert(element != null);
+    assert(canVisit(uri));
+  }
+
+  bool canVisit(Uri uri) => uri.path.startsWith('isolate-reconnect');
 }
 
 class MetricsPage extends Page {
   // Page state, retained as long as ObservatoryApplication.
   String selectedMetricId;
 
   final Map<int, MetricPoller> pollers = new Map<int, MetricPoller>();
 
   // 8 seconds, 4 seconds, 2 seconds, 1 second, and one hundred milliseconds.
   static final List<int> POLL_PERIODS = [8000,
@@ skipping 40 matching lines @@
   void _visit(Uri uri) {
     assert(element != null);
     assert(canVisit(uri));
     app.vm.getIsolate(uri.queryParameters['isolateId']).then((i) {
       (element as MetricsPageElement).isolate = i;
     });
   }
 
   bool canVisit(Uri uri) => uri.path == 'metrics';
 }