Make VM event streams look like real dart streams.

runtime/observatory/lib/src/elements/debugger.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.
 
 library debugger_page_element;
 
 import 'dart:async';
 import 'dart:html';
 import 'observatory_element.dart';
-import 'package:observatory/app.dart';
 import 'package:observatory/cli.dart';
 import 'package:observatory/debugger.dart';
 import 'package:observatory/service.dart';
 import 'package:polymer/polymer.dart';
 
 // TODO(turnidge): Move Debugger, DebuggerCommand to debugger library.
 abstract class DebuggerCommand extends Command {
   ObservatoryDebugger debugger;
 
   DebuggerCommand(this.debugger, name, children)
@@ skipping 893 matching lines @@
       _isolate.reload().then((response) {
         // TODO(turnidge): Currently the debugger relies on all libs
         // being loaded.  Fix this.
         var pending = [];
         for (var lib in _isolate.libraries) {
           if (!lib.loaded) {
             pending.add(lib.load());
           }
         }
         Future.wait(pending).then((_) {
-          if (_subscription == null) {
-            _subscription = vm.events.stream.listen(_onEvent);
-          }
           _refreshStack(isolate.pauseEvent).then((_) {
             reportStatus();
           });
         }).catchError((_) {
           // Error loading libraries, try and display stack.
           _refreshStack(isolate.pauseEvent).then((_) {
             reportStatus();
           });
         });
       });
     } else {
       reportStatus();
     }
   }
 
   set isolate(Isolate iso) {
     // Setting the page's isolate will trigger updateIsolate to be called.
     //
     // TODO(turnidge): Rework ownership of the ObservatoryDebugger in another
     // change.
     page.isolate = iso;
   }
   Isolate get isolate => _isolate;
   Isolate _isolate;
-  var _subscription;
 
   void init() {
     console.newline();
     console.printBold("Type 'h' for help");
     // Wait a bit and if polymer still hasn't set up the isolate,
     // report this to the user.
     new Timer(const Duration(seconds:1), () {
       if (isolate == null) {
         reportStatus();
       }
@@ skipping 111 matching lines @@
       if (bpt.resolved) {
         console.print(
             'Breakpoint ${bpId} ${verb} at ${script.name}:${line}:${col}');
       } else {
         console.print(
             'Future breakpoint ${bpId} ${verb} at ${script.name}:${line}:${col}');
       }
     });
   }
 
-  void _onEvent(ServiceEvent event) {
+  void onEvent(ServiceEvent event) {
     switch(event.kind) {
       case ServiceEvent.kIsolateStart:
         {
           var iso = event.owner;
           console.print(
               "Isolate ${iso.number} '${iso.name}' has been created");
         }
         break;
 
       case ServiceEvent.kIsolateExit:
@@ skipping 125 matching lines @@
     return cmd.historyPrev(command);
   }
 
   String historyNext(String command) {
     return cmd.historyNext(command);
   }
 }
 
 @CustomTag('debugger-page')
 class DebuggerPageElement extends ObservatoryElement {
-  @published ObservatoryApplication app;
   @published Isolate isolate;
 
   isolateChanged(oldValue) {
     if (isolate != null) {
       debugger.updateIsolate(isolate);
     }
   }
   ObservatoryDebugger debugger = new ObservatoryDebugger();
 
   DebuggerPageElement.created() : super.created() {
     debugger.page = this;
   }
 
+  Future<StreamSubscription> _isolateSubscriptionFuture;
+  Future<StreamSubscription> _debugSubscriptionFuture;
+
   @override
   void attached() {
     super.attached();
 
     var navbarDiv = $['navbarDiv'];
     var stackDiv = $['stackDiv'];
     var splitterDiv = $['splitterDiv'];
     var cmdDiv = $['commandDiv'];
 
     int navbarHeight = navbarDiv.clientHeight;
     int splitterHeight = splitterDiv.clientHeight;
     int cmdHeight = cmdDiv.clientHeight;
 
     int windowHeight = window.innerHeight;
     int fixedHeight = navbarHeight + splitterHeight + cmdHeight;
     int available = windowHeight - fixedHeight;
     int stackHeight = available ~/ 1.6;
     stackDiv.style.setProperty('height', '${stackHeight}px');
 
     // Wire the debugger object to the stack, console, and command line.
     var stackElement = $['stackElement'];
     debugger.stackElement = stackElement;
     stackElement.debugger = debugger;
     debugger.console = $['console'];
     debugger.input = $['commandline'];
     debugger.input.debugger = debugger;
     debugger.init();
+
+    _isolateSubscriptionFuture =
+        app.vm.listenEventStream(VM.kIsolateStream, debugger.onEvent);
+    _debugSubscriptionFuture =
+        app.vm.listenEventStream(VM.kDebugStream, debugger.onEvent);
+  }
+
+  @override
+  void detached() {
+    cancelFutureSubscription(_isolateSubscriptionFuture);
+    _isolateSubscriptionFuture = null;
+    cancelFutureSubscription(_debugSubscriptionFuture);
+    _debugSubscriptionFuture = null;
+    super.detached();
   }
 }
 
 @CustomTag('debugger-stack')
 class DebuggerStackElement extends ObservatoryElement {
   @published Isolate isolate;
   @observable bool hasStack = false;
   @observable bool hasMessages = false;
   @observable bool isSampled = false;
   @observable int currentFrame;
@@ skipping 440 matching lines @@
       });
   }
 
   void focus() {
     $['textBox'].focus();
   }
 
   DebuggerInputElement.created() : super.created();
 }