fix(dialog): leaking component instance references

Fixes a memory leak in the dialog, which was causing it to keep references to the user's instantiated dialog in memory forever. It was due to:
1. The portal class wasn't invoking the cleanup function if it didn't have attached content.
2. The dialog ref was keeping the reference after the dialog is closed. There is also a leak related to dialog refs which will be addressed separately.

Fixes #2734.

src/lib/core/portal/portal-directives.ts

@@ -70,7 +70,7 @@ export class PortalHostDirective extends BasePortalHost implements OnDestroy {
   }
 
   ngOnDestroy() {
-    this.dispose();
+    super.dispose();
   }
 
   /**
@@ -93,7 +93,7 @@ export class PortalHostDirective extends BasePortalHost implements OnDestroy {
         componentFactory, viewContainerRef.length,
         portal.injector || viewContainerRef.parentInjector);
 
-    this.setDisposeFn(() => ref.destroy());
+    super.setDisposeFn(() => ref.destroy());
     return ref;
   }
 
@@ -105,7 +105,7 @@ export class PortalHostDirective extends BasePortalHost implements OnDestroy {
     portal.setAttachedHost(this);
 
     this._viewContainerRef.createEmbeddedView(portal.templateRef);
-    this.setDisposeFn(() => this._viewContainerRef.clear());
+    super.setDisposeFn(() => this._viewContainerRef.clear());
 
     // TODO(jelbourn): return locals from view
     return new Map<string, any>();
@@ -114,11 +114,11 @@ export class PortalHostDirective extends BasePortalHost implements OnDestroy {
   /** Detaches the currently attached Portal (if there is one) and attaches the given Portal. */
   private _replaceAttachedPortal(p: Portal<any>): void {
     if (this.hasAttached()) {
-      this.detach();
+      super.detach();
     }
 
     if (p) {
-      this.attach(p);
+      super.attach(p);
       this._portal = p;
     }
   }

src/lib/core/portal/portal.spec.ts

@@ -278,6 +278,17 @@ describe('Portals', () => {
       expect(someDomElement.innerHTML)
           .toBe('', 'Expected the DomPortalHost to be empty after detach');
     });
+
+    it('should call the dispose function even if the host has no attached content', () => {
+      let spy = jasmine.createSpy('host dispose spy');
+
+      expect(host.hasAttached()).toBe(false, 'Expected host not to have attached content.');
+
+      host.setDisposeFn(spy);
+      host.dispose();
+
+      expect(spy).toHaveBeenCalled();
+    });
   });
 });
 

src/lib/core/portal/portal.ts

@@ -162,12 +162,12 @@ export abstract class BasePortalHost implements PortalHost {
   private _isDisposed: boolean = false;
 
   /** Whether this host has an attached portal. */
-  hasAttached() {
-    return this._attachedPortal != null;
+  hasAttached(): boolean {
+    return !!this._attachedPortal;
   }
 
   attach(portal: Portal<any>): any {
-    if (portal == null) {
+    if (!portal) {
       throw new NullPortalError();
     }
 
@@ -195,24 +195,31 @@ export abstract class BasePortalHost implements PortalHost {
   abstract attachTemplatePortal(portal: TemplatePortal): Map<string, any>;
 
   detach(): void {
-    if (this._attachedPortal) { this._attachedPortal.setAttachedHost(null); }
-
-    this._attachedPortal = null;
-    if (this._disposeFn != null) {
-      this._disposeFn();
-      this._disposeFn = null;
+    if (this._attachedPortal) {
+      this._attachedPortal.setAttachedHost(null);
+      this._attachedPortal = null;
     }
+
+    this._invokeDisposeFn();
   }
 
   dispose() {
     if (this.hasAttached()) {
       this.detach();
     }
 
+    this._invokeDisposeFn();
     this._isDisposed = true;
   }
 
   setDisposeFn(fn: () => void) {
     this._disposeFn = fn;
   }
+
+  private _invokeDisposeFn() {
+    if (this._disposeFn) {
+      this._disposeFn();
+      this._disposeFn = null;
+    }
+  }
 }

src/lib/dialog/dialog-ref.ts

@@ -31,6 +31,7 @@ export class MdDialogRef<T> {
           this._overlayRef.dispose();
           this._afterClosed.next(this._result);
           this._afterClosed.complete();
+          this.componentInstance = null;
         }
       });
   }

src/lib/dialog/dialog.spec.ts

@@ -345,6 +345,19 @@ describe('MdDialog', () => {
     });
   });
 
+  it('should not keep a reference to the component after the dialog is closed', async(() => {
+    let dialogRef = dialog.open(PizzaMsg);
+
+    expect(dialogRef.componentInstance).toBeTruthy();
+
+    dialogRef.close();
+    viewContainerFixture.detectChanges();
+
+    viewContainerFixture.whenStable().then(() => {
+      expect(dialogRef.componentInstance).toBeFalsy('Expected reference to have been cleared.');
+    });
+  }));
+
   describe('disableClose option', () => {
     it('should prevent closing via clicks on the backdrop', () => {
       dialog.open(PizzaMsg, {