An accessible click on a menu list option should toggle menu list popup

The options in an HTML select element are present in the
accessibility tree even when the popup is not visible. As a
result it's possible for AT such as ChromeVox to fire a click
event on an option. However, since the popup is collapsed, the
expected behavior is for the menu to pop open - then clicking it
again should close it.

This wasn't implemented before because most AT only sends the
click event to the <select> element when it's collapsed.

Bug: 1046087
Change-Id: Ic110efc771490035e24041362211dc5c61585248
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2025323Reviewed-by: David Tseng <dtseng@chromium.org>
Commit-Queue: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#736123}

third_party/blink/renderer/modules/accessibility/ax_menu_list_option.cc

@@ -141,6 +141,22 @@ AccessibilitySelectedState AXMenuListOption::IsSelected() const {
                                              : kSelectedStateFalse);
 }
 
+bool AXMenuListOption::OnNativeClickAction() {
+  if (!element_)
+    return false;
+
+  // Clicking on an option within a menu list should first select that item,
+  // then toggle whether the menu list is showing.
+  element_->SetSelected(true);
+
+  // Calling OnNativeClickAction on the parent select element will toggle
+  // it open or closed.
+  if (ParentObject() && ParentObject()->IsMenuListPopup())
+    return ParentObject()->OnNativeClickAction();
+
+  return AXMockObject::OnNativeClickAction();
+}
+
 bool AXMenuListOption::OnNativeSetSelectedAction(bool b) {
   if (!element_ || !CanSetSelectedAttribute())
     return false;

third_party/blink/renderer/modules/accessibility/ax_menu_list_option.h

@@ -59,6 +59,7 @@ class AXMenuListOption final : public AXMockObject {
   bool IsVisible() const override;
   bool IsOffScreen() const override;
   AccessibilitySelectedState IsSelected() const override;
+  bool OnNativeClickAction() override;
   bool OnNativeSetSelectedAction(bool) override;
 
   void GetRelativeBounds(AXObject** out_container,