fix(menu): not handling keyboard events when opened by mouse

Fixes the menu keyboard interactions not working when it is opened by a click.

Fixes angular#4991.

src/lib/menu/menu-trigger.ts

@@ -161,10 +161,15 @@ export class MdMenuTrigger implements AfterViewInit, OnDestroy {
   private _initMenu(): void {
     this._setIsMenuOpen(true);
 
-    // Should only set focus if opened via the keyboard, so keyboard users can
-    // can easily navigate menu items. According to spec, mouse users should not
-    // see the focus style.
-    if (!this._openedByMouse) {
+    // If the menu was opened by mouse, we focus the root node, which allows for the keyboard
+    // interactions to work. Otherwise, if the menu was opened by keyboard, we focus the first item.
+    if (this._openedByMouse) {
+      let rootNode = this._overlayRef.overlayElement.firstElementChild as HTMLElement;
+
+      if (rootNode) {
+        rootNode.focus();
+      }
+    } else {
       this.menu.focusFirstItem();
     }
   }

src/lib/menu/menu.html

@@ -1,6 +1,6 @@
 <ng-template>
   <div class="mat-menu-panel" [ngClass]="_classList" (keydown)="_handleKeydown($event)"
-    (click)="_emitCloseEvent()" [@transformMenu]="'showing'">
+    (click)="_emitCloseEvent()" [@transformMenu]="'showing'" tabindex="-1">
     <div class="mat-menu-content" [@fadeInItems]="'showing'">
       <ng-content></ng-content>
     </div>

src/lib/menu/menu.scss

@@ -12,6 +12,7 @@ $mat-menu-vertical-padding: 8px !default;
   @include mat-menu-base();
   @include mat-menu-positions();
   max-height: calc(100vh - #{$mat-menu-item-height});
+  outline: 0;
 
   @include cdk-high-contrast {
     outline: solid 1px;

src/lib/menu/menu.spec.ts

@@ -21,7 +21,7 @@ import {OverlayContainer} from '../core/overlay/overlay-container';
 import {Dir, LayoutDirection} from '../core/rtl/dir';
 import {extendObject} from '../core/util/object-extend';
 import {ESCAPE} from '../core/keyboard/keycodes';
-import {dispatchKeyboardEvent} from '../core/testing/dispatch-events';
+import {dispatchKeyboardEvent, dispatchFakeEvent} from '../core/testing/dispatch-events';
 
 
 describe('MdMenu', () => {
@@ -134,6 +134,23 @@ describe('MdMenu', () => {
     expect(panel.classList).toContain('custom-two');
   });
 
+  it('should focus the menu panel root node when it was opened by mouse', () => {
+    const fixture = TestBed.createComponent(SimpleMenu);
+
+    fixture.detectChanges();
+
+    const triggerEl = fixture.componentInstance.triggerEl.nativeElement;
+
+    dispatchFakeEvent(triggerEl, 'mousedown');
+    triggerEl.click();
+    fixture.detectChanges();
+
+    const panel = overlayContainerElement.querySelector('.mat-menu-panel');
+
+    expect(panel).toBeTruthy('Expected the panel to be rendered.');
+    expect(document.activeElement).toBe(panel, 'Expected the panel to be focused.');
+  });
+
   describe('positions', () => {
     let fixture: ComponentFixture<PositionedMenu>;
     let panel: HTMLElement;