Fix test exceptions on IE.

Author: crisbeto

src/lib/dialog/dialog-container.ts

@@ -59,7 +59,7 @@ export class MdDialogContainer extends BasePortalHost implements OnDestroy {
   @ViewChild(FocusTrap) _focusTrap: FocusTrap;
 
   /** Element that was focused before the dialog was opened. Save this to restore upon close. */
-  private _elementFocusedBeforeDialogWasOpened: Element = null;
+  private _elementFocusedBeforeDialogWasOpened: HTMLElement = null;
 
   /** The dialog configuration. */
   dialogConfig: MdDialogConfig;
@@ -89,7 +89,7 @@ export class MdDialogContainer extends BasePortalHost implements OnDestroy {
     // ready in instances where change detection has to run first. To deal with this, we simply
     // wait for the microtask queue to be empty.
     this._ngZone.onMicrotaskEmpty.first().subscribe(() => {
-      this._elementFocusedBeforeDialogWasOpened = document.activeElement;
+      this._elementFocusedBeforeDialogWasOpened = document.activeElement as HTMLElement;
       this._focusTrap.focusFirstTabbableElement();
     });
 
@@ -113,6 +113,7 @@ export class MdDialogContainer extends BasePortalHost implements OnDestroy {
       if (toFocus && 'focus' in toFocus) {
         toFocus.focus();
       }
+
       this._onAnimationStateChange.complete();
     });
   }