fix(core): always remove DOM listeners and stream subscriptions

This is needed to prevent memory leaks. The DOM
listeners don’t need to be removed for simple examples,
but a big internal app shows memory leaks because of them.

BREAKING CHANGE:
- `Renderer.listen` now has to return a function that
  removes the event listener.

modules/angular2/src/platform/dom/dom_renderer.ts

@@ -155,9 +155,9 @@ export class DomRenderer implements Renderer {
     }
   }
 
-  listen(renderElement: any, name: string, callback: Function) {
-    this._rootRenderer.eventManager.addEventListener(renderElement, name,
-                                                     decoratePreventDefault(callback));
+  listen(renderElement: any, name: string, callback: Function): Function {
+    return this._rootRenderer.eventManager.addEventListener(renderElement, name,
+                                                            decoratePreventDefault(callback));
   }
 
   listenGlobal(target: string, name: string, callback: Function): Function {

modules/angular2/src/platform/dom/events/dom_events.ts

@@ -8,10 +8,11 @@ export class DomEventsPlugin extends EventManagerPlugin {
   // events.
   supports(eventName: string): boolean { return true; }
 
-  addEventListener(element: HTMLElement, eventName: string, handler: Function) {
+  addEventListener(element: HTMLElement, eventName: string, handler: Function): Function {
     var zone = this.manager.getZone();
     var outsideHandler = (event) => zone.run(() => handler(event));
-    this.manager.getZone().runOutsideAngular(() => { DOM.on(element, eventName, outsideHandler); });
+    return this.manager.getZone().runOutsideAngular(
+        () => DOM.onAndCancel(element, eventName, outsideHandler));
   }
 
   addGlobalEventListener(target: string, eventName: string, handler: Function): Function {
@@ -19,6 +20,6 @@ export class DomEventsPlugin extends EventManagerPlugin {
     var zone = this.manager.getZone();
     var outsideHandler = (event) => zone.run(() => handler(event));
     return this.manager.getZone().runOutsideAngular(
-        () => { return DOM.onAndCancel(element, eventName, outsideHandler); });
+        () => DOM.onAndCancel(element, eventName, outsideHandler));
   }
 }

modules/angular2/src/platform/dom/events/event_manager.ts

@@ -16,9 +16,9 @@ export class EventManager {
     this._plugins = ListWrapper.reversed(plugins);
   }
 
-  addEventListener(element: HTMLElement, eventName: string, handler: Function) {
+  addEventListener(element: HTMLElement, eventName: string, handler: Function): Function {
     var plugin = this._findPluginFor(eventName);
-    plugin.addEventListener(element, eventName, handler);
+    return plugin.addEventListener(element, eventName, handler);
   }
 
   addGlobalEventListener(target: string, eventName: string, handler: Function): Function {
@@ -47,7 +47,7 @@ export class EventManagerPlugin {
   // That is equivalent to having supporting $event.target
   supports(eventName: string): boolean { return false; }
 
-  addEventListener(element: HTMLElement, eventName: string, handler: Function) {
+  addEventListener(element: HTMLElement, eventName: string, handler: Function): Function {
     throw "not implemented";
   }
 

modules/angular2/src/platform/dom/events/hammer_gestures.ts

@@ -15,17 +15,18 @@ export class HammerGesturesPlugin extends HammerGesturesPluginCommon {
     return true;
   }
 
-  addEventListener(element: HTMLElement, eventName: string, handler: Function) {
+  addEventListener(element: HTMLElement, eventName: string, handler: Function): Function {
     var zone = this.manager.getZone();
     eventName = eventName.toLowerCase();
 
-    zone.runOutsideAngular(function() {
+    return zone.runOutsideAngular(function() {
       // Creating the manager bind events, must be done outside of angular
       var mc = new Hammer(element);
       mc.get('pinch').set({enable: true});
       mc.get('rotate').set({enable: true});
-
-      mc.on(eventName, function(eventObj) { zone.run(function() { handler(eventObj); }); });
+      var handler = function(eventObj) { zone.run(function() { handler(eventObj); }); };
+      mc.on(eventName, handler);
+      return () => { mc.off(eventName, handler); };
     });
   }
 }

modules/angular2/src/platform/dom/events/key_events.ts

@@ -27,14 +27,15 @@ export class KeyEventsPlugin extends EventManagerPlugin {
     return isPresent(KeyEventsPlugin.parseEventName(eventName));
   }
 
-  addEventListener(element: HTMLElement, eventName: string, handler: Function) {
+  addEventListener(element: HTMLElement, eventName: string, handler: Function): Function {
     var parsedEvent = KeyEventsPlugin.parseEventName(eventName);
 
     var outsideHandler = KeyEventsPlugin.eventCallback(
         element, StringMapWrapper.get(parsedEvent, 'fullKey'), handler, this.manager.getZone());
 
-    this.manager.getZone().runOutsideAngular(() => {
-      DOM.on(element, StringMapWrapper.get(parsedEvent, 'domEventName'), outsideHandler);
+    return this.manager.getZone().runOutsideAngular(() => {
+      return DOM.onAndCancel(element, StringMapWrapper.get(parsedEvent, 'domEventName'),
+                             outsideHandler);
     });
   }