(fix): make sure no leaking subscription

make sure subscription on fromEvent observable is unsubscribed when the
component is destroyed

Author: erhise

src/lib/sidenav/drawer.ts

@@ -206,6 +206,9 @@ export class MatDrawer implements AfterContentInit, AfterContentChecked, OnDestr
     );
   }
 
+  /** Emits when the component is destroyed. */
+  private readonly _destroyed = new Subject<void>();
+
   /** Event emitted when the drawer's position changes. */
   // tslint:disable-next-line:no-output-on-prefix
   @Output('positionChanged') onPositionChanged: EventEmitter<void> = new EventEmitter<void>();
@@ -249,7 +252,8 @@ export class MatDrawer implements AfterContentInit, AfterContentChecked, OnDestr
      */
     this._ngZone.runOutsideAngular(() => {
         fromEvent<KeyboardEvent>(this._elementRef.nativeElement, 'keydown').pipe(
-            filter(event => event.keyCode === ESCAPE && !this.disableClose)
+            filter(event => event.keyCode === ESCAPE && !this.disableClose),
+            takeUntil(this._destroyed)
         ).subscribe(event => this._ngZone.run(() => {
             this.close();
             event.stopPropagation();
@@ -314,6 +318,7 @@ export class MatDrawer implements AfterContentInit, AfterContentChecked, OnDestr
     if (this._focusTrap) {
       this._focusTrap.destroy();
     }
+    this._destroyed.next();
   }
 
   /**