fix(slide-toggle): clicks not landing correctly in some cases on Chrome

Any time the slide toggle host receives focus we forward it immediately to the underlying `input` element. This bouncing around of focus seems to interrupt click events in some cases on Chrome. These changes make it so that we only forward focus for events originating from the keyboard or programmatically.

Fixes #18269.

Author: crisbeto

src/material/slide-toggle/BUILD.bazel

@@ -56,6 +56,7 @@ ng_test_library(
     ),
     deps = [
         ":slide-toggle",
+        "//src/cdk/a11y",
         "//src/cdk/bidi",
         "//src/cdk/observers",
         "//src/cdk/testing/private",

src/material/slide-toggle/slide-toggle.spec.ts

@@ -9,9 +9,11 @@ import {
   flushMicrotasks,
   TestBed,
   tick,
+  inject,
 } from '@angular/core/testing';
 import {FormControl, FormsModule, NgModel, ReactiveFormsModule} from '@angular/forms';
 import {By} from '@angular/platform-browser';
+import {FocusMonitor} from '@angular/cdk/a11y';
 import {MatSlideToggle, MatSlideToggleChange, MatSlideToggleModule} from './index';
 import {MAT_SLIDE_TOGGLE_DEFAULT_OPTIONS} from './slide-toggle-config';
 
@@ -310,6 +312,19 @@ describe('MatSlideToggle without forms', () => {
       expect(document.activeElement).toBe(inputElement);
     });
 
+    it('should not manually move focus to underlying input when focus comes from mouse or touch',
+      inject([FocusMonitor], (focusMonitor: FocusMonitor) => {
+        expect(document.activeElement).not.toBe(inputElement);
+
+        focusMonitor.focusVia(slideToggleElement, 'mouse');
+        fixture.detectChanges();
+        expect(document.activeElement).not.toBe(inputElement);
+
+        focusMonitor.focusVia(slideToggleElement, 'touch');
+        fixture.detectChanges();
+        expect(document.activeElement).not.toBe(inputElement);
+      }));
+
     it('should set a element class if labelPosition is set to before', () => {
       expect(slideToggleElement.classList).not.toContain('mat-slide-toggle-label-before');
 

src/material/slide-toggle/slide-toggle.ts

@@ -91,7 +91,6 @@ const _MatSlideToggleMixinBase:
     '[class.mat-disabled]': 'disabled',
     '[class.mat-slide-toggle-label-before]': 'labelPosition == "before"',
     '[class._mat-animation-noopable]': '_animationMode === "NoopAnimations"',
-    '(focus)': '_inputElement.nativeElement.focus()',
   },
   templateUrl: 'slide-toggle.html',
   styleUrls: ['slide-toggle.css'],
@@ -193,7 +192,13 @@ export class MatSlideToggle extends _MatSlideToggleMixinBase implements OnDestro
     this._focusMonitor
       .monitor(this._elementRef, true)
       .subscribe(focusOrigin => {
-        if (!focusOrigin) {
+        // Only forward focus manually when it was received programmatically or through the
+        // keyboard. We should not do this for mouse/touch focus for two reasons:
+        // 1. It can prevent clicks from landing in Chrome (see #18269).
+        // 2. They're already handled by the wrapping `label` element.
+        if (focusOrigin === 'keyboard' || focusOrigin === 'program') {
+          this._inputElement.nativeElement.focus();
+        } else if (!focusOrigin) {
           // When a focused element becomes disabled, the browser *immediately* fires a blur event.
           // Angular does not expect events to be raised during change detection, so any state
           // change (such as a form control's 'ng-touched') will cause a changed-after-checked