Add isolate tag-profile and better handling of errors

runtime/vm/service/running_isolates.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.
 
 part of vmservice;
 
 class RunningIsolates implements MessageRouter {
   final Map<int, RunningIsolate> isolates = new Map<int, RunningIsolate>();
+  int _rootPortId;
 
   RunningIsolates();
 
   void isolateStartup(int portId, SendPort sp, String name) {
+    if (_rootPortId == null) {
+      _rootPortId = portId;
+    }
     var ri = new RunningIsolate(portId, sp, name);
     isolates[portId] = ri;
   }
 
   void isolateShutdown(int portId, SendPort sp) {
+    if (_rootPortId == portId) {
+      _rootPortId = null;
+    }
     isolates.remove(portId);
   }
 
   Future<String> route(Message message) {
     if (message.path.length == 0) {
       message.setErrorResponse('No path.');
       return message.response;
     }
     if (message.path[0] != 'isolates') {
       message.setErrorResponse('Path must begin with /isolates/');
       return message.response;
     }
     if (message.path.length < 2) {
       message.setErrorResponse('An isolate id must be provided');
       return message.response;
     }
     var isolateId;
-    try {
-      isolateId = int.parse(message.path[1]);
-    } catch (e) {
-      message.setErrorResponse('Could not parse isolate id: $e');
-      return message.response;
+    if ((message.path[1] == 'root') && (_rootPortId != null)) {
+      isolateId = _rootPortId;

[turnidge, 2014/03/24 20:22:13]

so isolates/root is an alias to whatever the root isolate's id is?

Not sure that this works so well, post my change.  Whenever we see an isolate we
don't recognize, we reload the VM rather than just trusting the id and reloading
the isolate.  You may want to drop this feature and we can add it later.

Another option is to suport "root" in the Observatory itself.

[Cutch, 2014/03/25 14:39:06]

This alias will never been seen by Observatory, it's primarily useful for
testing from the command line. I'd like to keep this in for now.

+    } else {
+      try {
+        isolateId = int.parse(message.path[1]);
+      } catch (e) {
+        message.setErrorResponse('Could not parse isolate id: $e');
+        return message.response;
+      }
     }
+    assert(isolateId != null);
     var isolate = isolates[isolateId];
     if (isolate == null) {
       message.setErrorResponse('Cannot find isolate id: $isolateId');
       return message.response;
     }
     // Consume '/isolates/isolateId'
     message.path.removeRange(0, 2);
     return isolate.route(message);
   }
 }