fix(slider, drawer): unsubscribe from directionaly change subject (#6907)

If a slider component will be destroyed, the `ngOnDestroy` hook calls `_directionality.change.unsubscribe()`, which means that the `unsubscribe` method is called on the `EventEmitter` instead of the actual `Subscription`. This causes the `EventEmitter` to be kind of "completed", which then means that there will be errors if `emit()` is called again (https://github.com/ReactiveX/rxjs/blob/master/src/Subject.ts#L96).

Also fixes that the drawer never unsubscribes from the `_dir.change` `EventEmitter`. This means that even if the component is destroyed, whenever the directionality changes, the drawer calls `validateDrawers()`.

Fixes #6892. Fixes #6903.

src/cdk/bidi/bidi.md

@@ -6,16 +6,25 @@ text direction (RTL or LTR);
 #### Example
 ```ts
 @Component({ ... }) 
-export class MyWidget {
+export class MyWidget implements OnDestroy {
+
+  /** Whether the widget is in RTL mode or not. */
   private isRtl: boolean;
   
+  /** Subscription to the Directionality change EventEmitter. */
+  private _dirChangeSubscription = Subscription.EMPTY;  
+  
   constructor(dir: Directionality) {
     this.isRtl = dir.value === 'rtl';
     
-    dir.change.subscribe(() => {
+    _dirChangeSubscription = dir.change.subscribe(() => {
       this.flipDirection();
     });
   }
+  
+  ngOnDestroy() {
+    this._dirChangeSubscription.unsubscribe();
+  }
 }  
 ```
 

src/lib/sidenav/drawer.ts

@@ -31,6 +31,7 @@ import {ESCAPE} from '../core/keyboard/keycodes';
 import {first, takeUntil, startWith} from '../core/rxjs/index';
 import {DOCUMENT} from '@angular/platform-browser';
 import {merge} from 'rxjs/observable/merge';
+import {Subscription} from 'rxjs/Subscription';
 
 
 /** Throws an exception when two MdDrawer are matching the same position. */
@@ -313,7 +314,7 @@ export class MdDrawer implements AfterContentInit, OnDestroy {
   changeDetection: ChangeDetectionStrategy.OnPush,
   encapsulation: ViewEncapsulation.None,
 })
-export class MdDrawerContainer implements AfterContentInit {
+export class MdDrawerContainer implements AfterContentInit, OnDestroy {
   @ContentChildren(MdDrawer) _drawers: QueryList<MdDrawer>;
 
   /** The drawer child with the `start` position. */
@@ -338,6 +339,9 @@ export class MdDrawerContainer implements AfterContentInit {
   private _left: MdDrawer | null;
   private _right: MdDrawer | null;
 
+  /** Subscription to the Directionality change EventEmitter. */
+  private _dirChangeSubscription = Subscription.EMPTY;
+
   /** Inline styles to be applied to the container. */
   _styles: { marginLeft: string; marginRight: string; transform: string; };
 
@@ -347,7 +351,7 @@ export class MdDrawerContainer implements AfterContentInit {
     // If a `Dir` directive exists up the tree, listen direction changes and update the left/right
     // properties to point to the proper start/end.
     if (_dir != null) {
-      _dir.change.subscribe(() => this._validateDrawers());
+      this._dirChangeSubscription = _dir.change.subscribe(() => this._validateDrawers());
     }
   }
 
@@ -361,6 +365,10 @@ export class MdDrawerContainer implements AfterContentInit {
     });
   }
 
+  ngOnDestroy() {
+    this._dirChangeSubscription.unsubscribe();
+  }
+
   /** Calls `open` of both start and end drawers */
   open(): void {
     this._drawers.forEach(drawer => drawer.open());

src/lib/slider/slider.ts

@@ -38,7 +38,7 @@ import {HammerInput} from '../core';
 import {FocusOrigin, FocusOriginMonitor} from '../core/style/focus-origin-monitor';
 import {CanDisable, mixinDisabled} from '../core/common-behaviors/disabled';
 import {CanColor, mixinColor} from '../core/common-behaviors/color';
-
+import {Subscription} from 'rxjs/Subscription';
 
 /**
  * Visually, a 30px separation between tick marks looks best. This is very subjective but it is
@@ -385,6 +385,9 @@ export class MdSlider extends _MdSliderMixinBase
   /** Decimal places to round to, based on the step amount. */
   private _roundLabelTo: number;
 
+  /** Subscription to the Directionality change EventEmitter. */
+  private _dirChangeSubscription = Subscription.EMPTY;
+
   /** The value of the slider when the slide start event fires. */
   private _valueOnSlideStart: number | null;
 
@@ -420,15 +423,15 @@ export class MdSlider extends _MdSliderMixinBase
           this._changeDetectorRef.detectChanges();
         });
     if (this._dir) {
-      this._dir.change.subscribe(() => this._changeDetectorRef.markForCheck());
+      this._dirChangeSubscription = this._dir.change.subscribe(() => {
+        this._changeDetectorRef.markForCheck();
+      });
     }
   }
 
   ngOnDestroy() {
     this._focusOriginMonitor.stopMonitoring(this._elementRef.nativeElement);
-    if (this._dir) {
-      this._dir.change.unsubscribe();
-    }
+    this._dirChangeSubscription.unsubscribe();
   }
 
   _onMouseenter() {