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

ui/views/controls/combobox/combobox_unittest.cc

Index: ui/views/controls/combobox/combobox_unittest.cc
diff --git a/ui/views/controls/combobox/combobox_unittest.cc b/ui/views/controls/combobox/combobox_unittest.cc
index 31a0c159ddf6c5a6e87c883b8220c7f486878131..bb10a1d54321c379a988bfea9276021f0908ff1f 100644
--- a/ui/views/controls/combobox/combobox_unittest.cc
+++ b/ui/views/controls/combobox/combobox_unittest.cc
@@ -9,6 +9,7 @@
 #include "base/macros.h"
 #include "base/strings/utf_string_conversions.h"
 #include "build/build_config.h"
+#include "ui/accessibility/ax_action_data.h"
 #include "ui/base/ime/input_method.h"
 #include "ui/base/ime/text_input_client.h"
 #include "ui/base/models/combobox_model.h"
@@ -642,6 +643,26 @@ TEST_F(ComboboxTest, NotifyOnClickWithSpaceKey) {
   EXPECT_FALSE(listener.on_perform_action_called());
 }
 
+// Test that accessibility action events show the combobox dropdown.
+TEST_F(ComboboxTest, ShowViaAccessibleAction) {
+  InitCombobox(nullptr, Combobox::STYLE_NORMAL);
+
+  ui::AXActionData data;
+  data.action = ui::AX_ACTION_DO_DEFAULT;
+
+  EXPECT_EQ(0, menu_show_count_);
+  combobox_->HandleAccessibleAction(data);
+  EXPECT_EQ(1, menu_show_count_);

[msw, 2017/06/29 19:26:12]

nit: test handling the action while the menu is showing?

[tapted, 2017/06/30 06:04:47]

doing this requires an interactive_ui_test (menus are tricksy). 

Combobox::ShowDropDownMenu() has handling for ensuring the old menu is closed
for the non-accessible actions.

+
+  combobox_->SetEnabled(false);
+  combobox_->HandleAccessibleAction(data);
+  EXPECT_EQ(1, menu_show_count_);  // No change.
+
+  data.action = ui::AX_ACTION_BLUR;

[msw, 2017/06/29 19:26:12]

Should this also test AX_ACTION_SHOW_CONTEXT_MENU, and increment/decrement?

[tapted, 2017/06/30 06:04:47]

AX_ACTION_SHOW_CONTEXT_MENU was actually tested in earlier patchsets, but we
decided context menus should not be a concept that views comboboxes should
handle -- it should do nothing. (For <select> elements in webcontent
AX_ACTION_SHOW_CONTEXT_MENU should show the regular page context menu.)

Except, for Mac, we want to expose NSAccessibilityShowMenuAction since it's not
exclusively used for context menus on native controls. (if this is a bug on
other platforms we can explore in a follow-up)

I guess it doesn't hurt to send AX_ACTION_SHOW_CONTEXT_MENU anyway, and verify
there's no change (done). However, a control doesn't usually expect to see
requests to handle actions it didn't first expose in its AXNodeData.

increment/decrement aren't exposed as actions on native Cocoa controls, so I
haven't added handling for it.

+  combobox_->HandleAccessibleAction(data);

[msw, 2017/06/29 19:26:12]

Maybe test other actions, like blur, before disabling the combobox?

[tapted, 2017/06/30 06:04:47]

Done.

+  EXPECT_EQ(1, menu_show_count_);  // No change.
+}
+
 TEST_F(ComboboxTest, NotifyOnClickWithSpaceKeyActionStyle) {
   InitCombobox(nullptr, Combobox::STYLE_ACTION);