refactor(core): drop unused SCHEDULER provider (#45102) (#45222)

The `SCHEDULER` provider was used previously when both ViewEngine and Ivy code was present. After some prior refactoring, all references to the `SCHEDULER` token were removed, but the token itself remains present in the `ApplicationModule`, which makes it non-tree-shakable.

This commit removes the `SCHEDULER` token as unused.

PR Close #45102

PR Close #45222

packages/core/src/application_module.ts

@@ -17,7 +17,6 @@ import {DEFAULT_CURRENCY_CODE, LOCALE_ID} from './i18n/tokens';
 import {ComponentFactoryResolver} from './linker';
 import {Compiler} from './linker/compiler';
 import {NgModule} from './metadata';
-import {SCHEDULER} from './render3/component_ref';
 import {NgZone} from './zone';
 
 declare const $localize: {locale?: string};
@@ -62,7 +61,6 @@ export const APPLICATION_MODULE_PROVIDERS: StaticProvider[] = [
     useClass: ApplicationRef,
     deps: [NgZone, Injector, ErrorHandler, ComponentFactoryResolver, ApplicationInitStatus]
   },
-  {provide: SCHEDULER, deps: [NgZone], useFactory: zoneSchedulerFactory},
   {
     provide: ApplicationInitStatus,
     useClass: ApplicationInitStatus,
@@ -78,27 +76,6 @@ export const APPLICATION_MODULE_PROVIDERS: StaticProvider[] = [
   {provide: DEFAULT_CURRENCY_CODE, useValue: USD_CURRENCY_CODE},
 ];
 
-/**
- * Schedule work at next available slot.
- *
- * In Ivy this is just `requestAnimationFrame`. For compatibility reasons when bootstrapped
- * using `platformRef.bootstrap` we need to use `NgZone.onStable` as the scheduling mechanism.
- * This overrides the scheduling mechanism in Ivy to `NgZone.onStable`.
- *
- * @param ngZone NgZone to use for scheduling.
- */
-export function zoneSchedulerFactory(ngZone: NgZone): (fn: () => void) => void {
-  let queue: (() => void)[] = [];
-  ngZone.onStable.subscribe(() => {
-    while (queue.length) {
-      queue.pop()!();
-    }
-  });
-  return function(fn: () => void) {
-    queue.push(fn);
-  };
-}
-
 /**
  * Configures the root injector for an app with
  * providers of `@angular/core` dependencies that `ApplicationRef` needs

packages/core/src/render3/component_ref.ts

@@ -7,7 +7,6 @@
  */
 
 import {ChangeDetectorRef as ViewEngine_ChangeDetectorRef} from '../change_detection/change_detector_ref';
-import {InjectionToken} from '../di/injection_token';
 import {Injector} from '../di/injector';
 import {InjectFlags} from '../di/interface/injector';
 import {ProviderToken} from '../di/provider_token';
@@ -36,7 +35,6 @@ import {createElementNode, writeDirectClass} from './node_manipulation';
 import {extractAttrsAndClassesFromSelector, stringifyCSSSelectorList} from './node_selector_matcher';
 import {enterView, leaveView} from './state';
 import {setUpAttributes} from './util/attrs_utils';
-import {defaultScheduler} from './util/misc_utils';
 import {getTNode} from './util/view_utils';
 import {RootViewRef, ViewRef} from './view_ref';
 
@@ -71,15 +69,6 @@ function getNamespace(elementName: string): string|null {
   return name === 'svg' ? SVG_NAMESPACE : (name === 'math' ? MATH_ML_NAMESPACE : null);
 }
 
-/**
- * A change detection scheduler token for {@link RootContext}. This token is the default value used
- * for the default `RootContext` found in the {@link ROOT_CONTEXT} token.
- */
-export const SCHEDULER = new InjectionToken<((fn: () => void) => void)>('SCHEDULER_TOKEN', {
-  providedIn: 'root',
-  factory: () => defaultScheduler,
-});
-
 function createChainedInjector(rootViewInjector: Injector, moduleInjector: Injector): Injector {
   return {
     get: <T>(token: ProviderToken<T>, notFoundValue?: T, flags?: InjectFlags): T => {