fix(cdk/overlay): don't close if scroll is coming from inside overlay (#26840)

Fixes that the `CloseScrollStrategy` was being triggered by scrollables inside the overlay.

Fixes #26780.

(cherry picked from commit 24fab99)

Author: crisbeto

src/cdk/overlay/scroll/close-scroll-strategy.spec.ts

@@ -1,14 +1,14 @@
 import {inject, TestBed, fakeAsync} from '@angular/core/testing';
-import {Component, NgZone} from '@angular/core';
+import {Component, ElementRef, NgZone} from '@angular/core';
 import {Subject} from 'rxjs';
 import {ComponentPortal, PortalModule} from '@angular/cdk/portal';
-import {ScrollDispatcher, ViewportRuler} from '@angular/cdk/scrolling';
+import {CdkScrollable, ScrollDispatcher, ViewportRuler} from '@angular/cdk/scrolling';
 import {Overlay, OverlayConfig, OverlayRef, OverlayModule, OverlayContainer} from '../index';
 
 describe('CloseScrollStrategy', () => {
   let overlayRef: OverlayRef;
   let componentPortal: ComponentPortal<MozarellaMsg>;
-  let scrolledSubject = new Subject();
+  let scrolledSubject = new Subject<CdkScrollable | undefined>();
   let scrollPosition: number;
 
   beforeEach(fakeAsync(() => {
@@ -55,6 +55,16 @@ describe('CloseScrollStrategy', () => {
     expect(overlayRef.detach).toHaveBeenCalled();
   });
 
+  it('should not detach if the scrollable is inside the overlay', () => {
+    overlayRef.attach(componentPortal);
+    spyOn(overlayRef, 'detach');
+
+    scrolledSubject.next({
+      getElementRef: () => new ElementRef(overlayRef.overlayElement),
+    } as CdkScrollable);
+    expect(overlayRef.detach).not.toHaveBeenCalled();
+  });
+
   it('should not attempt to detach the overlay after it has been detached', () => {
     overlayRef.attach(componentPortal);
     overlayRef.detach();

src/cdk/overlay/scroll/close-scroll-strategy.ts

@@ -10,6 +10,7 @@ import {ScrollStrategy, getMatScrollStrategyAlreadyAttachedError} from './scroll
 import {OverlayReference} from '../overlay-reference';
 import {Subscription} from 'rxjs';
 import {ScrollDispatcher, ViewportRuler} from '@angular/cdk/scrolling';
+import {filter} from 'rxjs/operators';
 
 /**
  * Config options for the CloseScrollStrategy.
@@ -49,7 +50,14 @@ export class CloseScrollStrategy implements ScrollStrategy {
       return;
     }
 
-    const stream = this._scrollDispatcher.scrolled(0);
+    const stream = this._scrollDispatcher.scrolled(0).pipe(
+      filter(scrollable => {
+        return (
+          !scrollable ||
+          !this._overlayRef.overlayElement.contains(scrollable.getElementRef().nativeElement)
+        );
+      }),
+    );
 
     if (this._config && this._config.threshold && this._config.threshold > 1) {
       this._initialScrollPosition = this._viewportRuler.getViewportScrollPosition().top;