https://codereview.chromium.org/2944083004

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/926329391ace2c7470f55b275988a09f4f1fd06b

commit 926329391ace2c7470f55b275988a09f4f1fd06b
Author: tapted <tapted@chromium.org>
Date: Mon Jul 03 04:16:16 2017

MacViews a11y: Support the "Show menu" action in Textfield and Combobox.

Currently Combobox and Textfield show no actions available to
accessibility.

For Mac, fix by mapping the default action (a click) to
NSAccessibilityPressAction and map AX_ACTION_SHOW_CONTEXT_MENU to
NSAccessibilityShowMenuAction. For comboboxes, both
NSAccessibilityPressAction and NSAccessibilityShowMenuAction show a
menu. For textfields, just the latter.

On Mac, automatically add and handle NSAccessibilityShowMenuAction for
controls that show a menu on press and don't have a separate context
menu.

For Textfields (and other controls using context menus), automatically
add ui::AX_ACTION_SHOW_CONTEXT_MENU for views that have a context menu
controller.

Comboboxes are trickier since the View that usually handles clicks is a
"TransparentButton". So handle these actions explicitly.

For menus triggered by a11y actions, there may be no mouse event. Cocoa
needs one to position the menu, so generate a dummy event for this.

BUG= 679247 ,  663536 ,  732655 

Review-Url: https://codereview.chromium.org/2944083004
Cr-Commit-Position: refs/heads/master@{#483939}

[modify] https://crrev.com/926329391ace2c7470f55b275988a09f4f1fd06b/ui/accessibility/platform/ax_platform_node_mac.h
[modify] https://crrev.com/926329391ace2c7470f55b275988a09f4f1fd06b/ui/accessibility/platform/ax_platform_node_mac.mm
[modify] https://crrev.com/926329391ace2c7470f55b275988a09f4f1fd06b/ui/views/accessibility/native_view_accessibility_base.cc
[modify] https://crrev.com/926329391ace2c7470f55b275988a09f4f1fd06b/ui/views/controls/combobox/combobox.cc
[modify] https://crrev.com/926329391ace2c7470f55b275988a09f4f1fd06b/ui/views/controls/combobox/combobox.h
[modify] https://crrev.com/926329391ace2c7470f55b275988a09f4f1fd06b/ui/views/controls/combobox/combobox_unittest.cc
[modify] https://crrev.com/926329391ace2c7470f55b275988a09f4f1fd06b/ui/views/controls/menu/menu_runner_impl_cocoa.mm
[modify] https://crrev.com/926329391ace2c7470f55b275988a09f4f1fd06b/ui/views/widget/native_widget_mac_accessibility_unittest.mm