refactor(tabs): constructor breaking changes for 8.0 (#15738)

Handles the constructor-related breaking changes for 8.0.

BREAKING CHANGES:
* `_ngZone` and `_platform` parameters in `MatTabHeader` constructor are now required.
* `changeDetectorRef` parameter in `MatTabBody` constructor is now required.

src/lib/schematics/ng-update/data/constructor-checks.ts

@@ -38,6 +38,10 @@ export const constructorChecks: VersionChanges<ConstructorChecksUpgradeData> = {
     {
       pr: 'https://github.com/angular/material2/pull/15722',
       changes: ['MatExpansionPanel']
+    },
+    {
+      pr: 'https://github.com/angular/material2/pull/15737',
+      changes: ['MatTabHeader', 'MatTabBody']
     }
   ],
 

src/lib/tabs/tab-body.ts

@@ -163,13 +163,10 @@ export class MatTabBody implements OnInit, OnDestroy {
 
   constructor(private _elementRef: ElementRef<HTMLElement>,
               @Optional() private _dir: Directionality,
-              /**
-               * @breaking-change 8.0.0 changeDetectorRef to be made required.
-               */
-              changeDetectorRef?: ChangeDetectorRef) {
+              changeDetectorRef: ChangeDetectorRef) {
 
-    if (this._dir && changeDetectorRef) {
-      this._dirChangeSubscription = this._dir.change.subscribe((dir: Direction) => {
+    if (_dir) {
+      this._dirChangeSubscription = _dir.change.subscribe((dir: Direction) => {
         this._computePositionAnimationState(dir);
         changeDetectorRef.markForCheck();
       });

src/lib/tabs/tab-header.ts

@@ -164,27 +164,18 @@ export class MatTabHeader extends _MatTabHeaderMixinBase
               private _changeDetectorRef: ChangeDetectorRef,
               private _viewportRuler: ViewportRuler,
               @Optional() private _dir: Directionality,
-              // @breaking-change 8.0.0 `_ngZone` and `_platforms` parameters to be made required.
-              private _ngZone?: NgZone,
-              private _platform?: Platform) {
+              private _ngZone: NgZone,
+              private _platform: Platform) {
     super();
 
-    const element = _elementRef.nativeElement;
-    const bindEvent = () => {
-      fromEvent(element, 'mouseleave')
+    // Bind the `mouseleave` event on the outside since it doesn't change anything in the view.
+    _ngZone.runOutsideAngular(() => {
+      fromEvent(_elementRef.nativeElement, 'mouseleave')
         .pipe(takeUntil(this._destroyed))
         .subscribe(() => {
           this._stopInterval();
         });
-    };
-
-    // @breaking-change 8.0.0 remove null check once _ngZone is made into a required parameter.
-    if (_ngZone) {
-      // Bind the `mouseleave` event on the outside since it doesn't change anything in the view.
-      _ngZone.runOutsideAngular(bindEvent);
-    } else {
-      bindEvent();
-    }
+    });
   }
 
   ngAfterContentChecked(): void {
@@ -310,16 +301,13 @@ export class MatTabHeader extends _MatTabHeaderMixinBase
     if (textContent !== this._currentTextContent) {
       this._currentTextContent = textContent;
 
-      const zoneCallback = () => {
+      // The content observer runs outside the `NgZone` by default, which
+      // means that we need to bring the callback back in ourselves.
+      this._ngZone.run(() => {
         this.updatePagination();
         this._alignInkBarToSelectedTab();
         this._changeDetectorRef.markForCheck();
-      };
-
-      // The content observer runs outside the `NgZone` by default, which
-      // means that we need to bring the callback back in ourselves.
-      // @breaking-change 8.0.0 Remove null check for `_ngZone` once it's a required parameter.
-      this._ngZone ? this._ngZone.run(zoneCallback) : zoneCallback();
+      });
     }
   }
 
@@ -410,8 +398,7 @@ export class MatTabHeader extends _MatTabHeaderMixinBase
     // position to be thrown off in some cases. We have to reset it ourselves to ensure that
     // it doesn't get thrown off. Note that we scope it only to IE and Edge, because messing
     // with the scroll position throws off Chrome 71+ in RTL mode (see #14689).
-    // @breaking-change 8.0.0 Remove null check for `platform`.
-    if (platform && (platform.TRIDENT || platform.EDGE)) {
+    if (platform.TRIDENT || platform.EDGE) {
       this._tabListContainer.nativeElement.scrollLeft = 0;
     }
   }

tools/public_api_guard/lib/tabs.d.ts

@@ -48,8 +48,7 @@ export declare class MatTabBody implements OnInit, OnDestroy {
     animationDuration: string;
     origin: number;
     position: number;
-    constructor(_elementRef: ElementRef<HTMLElement>, _dir: Directionality,
-    changeDetectorRef?: ChangeDetectorRef);
+    constructor(_elementRef: ElementRef<HTMLElement>, _dir: Directionality, changeDetectorRef: ChangeDetectorRef);
     _getLayoutDirection(): Direction;
     _isCenterPosition(position: MatTabBodyPositionState | string): boolean;
     _onTranslateTabStarted(event: AnimationEvent): void;
@@ -124,7 +123,7 @@ export declare class MatTabHeader extends _MatTabHeaderMixinBase implements Afte
     scrollDistance: number;
     readonly selectFocusedIndex: EventEmitter<number>;
     selectedIndex: number;
-    constructor(_elementRef: ElementRef, _changeDetectorRef: ChangeDetectorRef, _viewportRuler: ViewportRuler, _dir: Directionality, _ngZone?: NgZone | undefined, _platform?: Platform | undefined);
+    constructor(_elementRef: ElementRef, _changeDetectorRef: ChangeDetectorRef, _viewportRuler: ViewportRuler, _dir: Directionality, _ngZone: NgZone, _platform: Platform);
     _alignInkBarToSelectedTab(): void;
     _checkPaginationEnabled(): void;
     _checkScrollingControls(): void;