[vm] Don't enable the profiler by default. Enable the profiler at startup with --observe, or later …

runtime/observatory/lib/src/elements/cpu_profile.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 cpu_profile_element;
 
 import 'dart:async';
 import 'dart:html';
 import 'package:observatory/models.dart' as M;
 import 'package:observatory/src/elements/cpu_profile/virtual_tree.dart';
@@ skipping 92 matching lines @@
         new NavRefreshElement(queue: _r.queue)..onRefresh.listen(_refresh),
         new NavRefreshElement(label: 'Clear', queue: _r.queue)
           ..onRefresh.listen(_clearCpuProfile),
         new NavNotifyElement(_notifications, queue: _r.queue)
       ]),
     ];
     if (_progress == null) {
       children = content;
       return;
     }
-    content.add(new SampleBufferControlElement(_progress, _progressStream,
+    content.add(new SampleBufferControlElement(_vm, _progress, _progressStream,
         selectedTag: _tag, queue: _r.queue)
       ..onTagChange.listen((e) {
         _tag = e.element.selectedTag;
-        _request();
+        _request(forceFetch: true);
       }));
     if (_progress.status == M.SampleProfileLoadingStatus.loaded) {
       CpuProfileVirtualTreeElement tree;
       content.addAll([
         new BRElement(),
         new StackTraceTreeConfigElement(
             mode: _mode,
             direction: _direction,
             filter: _filter,
             queue: _r.queue)
@@ skipping 39 matching lines @@
     await _request(clear: true);
     e.element.disabled = false;
   }
 
   Future _refresh(e) async {
     e.element.disabled = true;
     await _request(forceFetch: true);
     e.element.disabled = false;
   }
 }