fix(tabs): move focus to first/last tabs using home/end (#9171)

Implements the ability to focus the first and last tabs using the home and end keys, based on the [accessibility guidelines](https://www.w3.org/TR/wai-aria-practices-1.1/#tabpanel).

src/lib/tabs/tab-header.spec.ts

@@ -1,10 +1,15 @@
 import {
-  async, ComponentFixture, TestBed, fakeAsync, tick, discardPeriodicTasks
+  async,
+  ComponentFixture,
+  TestBed,
+  fakeAsync,
+  tick,
+  discardPeriodicTasks,
 } from '@angular/core/testing';
 import {Component, ViewChild} from '@angular/core';
 import {CommonModule} from '@angular/common';
 import {By} from '@angular/platform-browser';
-import {ENTER, LEFT_ARROW, RIGHT_ARROW, SPACE} from '@angular/cdk/keycodes';
+import {ENTER, LEFT_ARROW, RIGHT_ARROW, SPACE, HOME, END} from '@angular/cdk/keycodes';
 import {PortalModule} from '@angular/cdk/portal';
 import {Direction, Directionality} from '@angular/cdk/bidi';
 import {dispatchFakeEvent, dispatchKeyboardEvent} from '@angular/cdk/testing';
@@ -136,6 +141,60 @@ describe('MatTabHeader', () => {
       expect(appComponent.selectedIndex).toBe(0);
       expect(spaceEvent.defaultPrevented).toBe(true);
     });
+
+    it('should move focus to the first tab when pressing HOME', () => {
+      appComponent.tabHeader.focusIndex = 3;
+      fixture.detectChanges();
+      expect(appComponent.tabHeader.focusIndex).toBe(3);
+
+      const tabListContainer = appComponent.tabHeader._tabListContainer.nativeElement;
+      const event = dispatchKeyboardEvent(tabListContainer, 'keydown', HOME);
+      fixture.detectChanges();
+
+      expect(appComponent.tabHeader.focusIndex).toBe(0);
+      expect(event.defaultPrevented).toBe(true);
+    });
+
+    it('should skip disabled items when moving focus using HOME', () => {
+      appComponent.tabHeader.focusIndex = 3;
+      appComponent.tabs[0].disabled = true;
+      fixture.detectChanges();
+      expect(appComponent.tabHeader.focusIndex).toBe(3);
+
+      const tabListContainer = appComponent.tabHeader._tabListContainer.nativeElement;
+      dispatchKeyboardEvent(tabListContainer, 'keydown', HOME);
+      fixture.detectChanges();
+
+      // Note that the second tab is disabled by default already.
+      expect(appComponent.tabHeader.focusIndex).toBe(2);
+    });
+
+    it('should move focus to the last tab when pressing END', () => {
+      appComponent.tabHeader.focusIndex = 0;
+      fixture.detectChanges();
+      expect(appComponent.tabHeader.focusIndex).toBe(0);
+
+      const tabListContainer = appComponent.tabHeader._tabListContainer.nativeElement;
+      const event = dispatchKeyboardEvent(tabListContainer, 'keydown', END);
+      fixture.detectChanges();
+
+      expect(appComponent.tabHeader.focusIndex).toBe(3);
+      expect(event.defaultPrevented).toBe(true);
+    });
+
+    it('should skip disabled items when moving focus using END', () => {
+      appComponent.tabHeader.focusIndex = 0;
+      appComponent.tabs[3].disabled = true;
+      fixture.detectChanges();
+      expect(appComponent.tabHeader.focusIndex).toBe(0);
+
+      const tabListContainer = appComponent.tabHeader._tabListContainer.nativeElement;
+      dispatchKeyboardEvent(tabListContainer, 'keydown', END);
+      fixture.detectChanges();
+
+      expect(appComponent.tabHeader.focusIndex).toBe(2);
+    });
+
   });
 
   describe('pagination', () => {

src/lib/tabs/tab-header.ts

@@ -7,7 +7,7 @@
  */
 
 import {Direction, Directionality} from '@angular/cdk/bidi';
-import {ENTER, LEFT_ARROW, RIGHT_ARROW, SPACE} from '@angular/cdk/keycodes';
+import {ENTER, LEFT_ARROW, RIGHT_ARROW, SPACE, HOME, END} from '@angular/cdk/keycodes';
 import {
   AfterContentChecked,
   AfterContentInit,
@@ -173,6 +173,14 @@ export class MatTabHeader extends _MatTabHeaderMixinBase
       case LEFT_ARROW:
         this._focusPreviousTab();
         break;
+      case HOME:
+        this._focusFirstTab();
+        event.preventDefault();
+        break;
+      case END:
+        this._focusLastTab();
+        event.preventDefault();
+        break;
       case ENTER:
       case SPACE:
         this.selectFocusedIndex.emit(this.focusIndex);
@@ -296,6 +304,26 @@ export class MatTabHeader extends _MatTabHeaderMixinBase
     this._moveFocus(this._getLayoutDirection() == 'ltr' ? -1 : 1);
   }
 
+  /** Focuses the first tab. */
+  private _focusFirstTab(): void {
+    for (let i = 0; i < this._labelWrappers.length; i++) {
+      if (this._isValidIndex(i)) {
+        this.focusIndex = i;
+        break;
+      }
+    }
+  }
+
+  /** Focuses the last tab. */
+  private _focusLastTab(): void {
+    for (let i = this._labelWrappers.length - 1; i > -1; i--) {
+      if (this._isValidIndex(i)) {
+        this.focusIndex = i;
+        break;
+      }
+    }
+  }
+
   /** The layout direction of the containing app. */
   _getLayoutDirection(): Direction {
     return this._dir && this._dir.value === 'rtl' ? 'rtl' : 'ltr';

src/lib/tabs/tabs.md

@@ -91,4 +91,7 @@ Tabs without text or labels should be given a meaningful label via `aria-label`
 |----------------------|----------------------------|
 | `LEFT_ARROW`         | Move focus to previous tab |
 | `RIGHT_ARROW`        | Move focus to next tab     |
+| `HOME`               | Move focus to first tab    |
+| `END`                | Move focus to last tab     |
+| `RIGHT_ARROW`        | Move focus to next tab     |
 | `SPACE` or `ENTER`   | Switch to focused tab      |