a11y: Add a11y information to views::Tab and manually ignore its a11y children.

ui/views/controls/tabbed_pane/tabbed_pane.cc

Index: ui/views/controls/tabbed_pane/tabbed_pane.cc
diff --git a/ui/views/controls/tabbed_pane/tabbed_pane.cc b/ui/views/controls/tabbed_pane/tabbed_pane.cc
index f36f68083227ffe0517ac13fcd8a703def3e8bff..49fd043e74ee2088e29022118efa6765244d75a0 100644
--- a/ui/views/controls/tabbed_pane/tabbed_pane.cc
+++ b/ui/views/controls/tabbed_pane/tabbed_pane.cc
@@ -27,6 +27,8 @@
 #include "ui/views/layout/layout_manager.h"
 #include "ui/views/widget/widget.h"
 
+namespace views {
+
 namespace {
 
 // TODO(markusheintz|msw): Use NativeTheme colors.
@@ -42,9 +44,22 @@ const gfx::Font::Weight kInactiveWeight = gfx::Font::Weight::NORMAL;
 
 const int kHarmonyTabStripTabHeight = 40;
 
-}  // namespace
+// views::Tab shouldn't expose any of its children in the a11y tree. Instead, it
+// should provide the a11y information itself. Normally, non-keyboard-focusable
+// children of keyboard-focusable parents are ignored, but Tabs only mark the
+// currently selected tab as keyboard-focusable. This means all unselected Tabs
+// expose their children to the a11y tree. To fix, manually ignore the children.
+class IgnoredLabel : public Label {

[Patti Lor, 2016/12/22 00:20:30]

Alternatively, we could add a method onto NativeViewAccessibility that sets a
flag saying an a11y element should be ignored. But I'm not sure if we'll need to
use that for any other cases than this, so not sure if it's that useful. Which
option do you prefer?

[tapted, 2016/12/22 00:50:09]

This looks good.

[Patti Lor, 2016/12/30 00:35:02]

Ok, thanks! :)

+ public:
+  IgnoredLabel(const base::string16& text, const gfx::FontList& font_list)

[tapted, 2016/12/22 00:50:08]

Can we call this TabLabel? And move the font_list initializer here. i.e. Do

explicit TabLabel(const std::string& tab_title)
  : Label(tab_title, ui::ResourceBundle.... ) {}

[Patti Lor, 2016/12/30 00:35:02]

Done.

+      : Label(text, font_list) {}
 
-namespace views {
+  void GetAccessibleNodeData(ui::AXNodeData* data) override {
+    data->role = ui::AX_ROLE_IGNORED;
+  }
+};
+
+}  // namespace
 
 // static
 const char TabbedPane::kViewClassName[] = "TabbedPane";
@@ -132,7 +147,7 @@ const char Tab::kViewClassName[] = "Tab";
 
 Tab::Tab(TabbedPane* tabbed_pane, const base::string16& title, View* contents)
     : tabbed_pane_(tabbed_pane),
-      title_(new Label(
+      title_(new IgnoredLabel(
           title,
           ui::ResourceBundle::GetSharedInstance().GetFontListWithDelta(
               ui::kLabelFontSizeDelta,
@@ -238,6 +253,12 @@ void Tab::SetState(TabState tab_state) {
   SchedulePaint();
 }
 
+void Tab::GetAccessibleNodeData(ui::AXNodeData* data) {
+  data->role = ui::AX_ROLE_TAB;
+  data->SetName(title()->text());
+  data->AddStateFlag(ui::AX_STATE_SELECTABLE);
+}

[tapted, 2016/12/22 00:50:08]

Are there more things we should add that NSSegmentedControl reports?

E.g. AX_STATE_CHECKED? AX_STATE_DISABLED (when !enabled()) or AX_STATE_PRESSED
(when the active tab), AX_SUPPORTED_ACTION_PRESS

[Patti Lor, 2016/12/30 00:35:02]

Good point - I've added ui::AX_STATE_SELECTED => AXSelected /
NSAccessibilitySelectedAttribute, but it makes no difference to VoiceOver (the
Cocoa version says "selected" when on a selected tab), and
accessibilitySelectedAttribute doesn't show up in the Accessibility Inspector
(checked Sierra + El Capitan). I've checked all the other NSAccessibility
attributes, and doesn't seem to be a similar NSAccessibility attribute that
looks like I can use to say "this tab of radio button role is already selected"
to get VO to behave properly. :(

Instead of AXSelectedAttribute, Cocoa is using AXValue to show whether the tab
is selected (it shows 0 or 1), which I have copied. Cocoa's version also doesn't
allow you to edit the AXValue of a tab (they let you click one using
"NSAccessibilityPressAction", but we don't have any NSAccessibility actions
implemented for Views atm), but I've deviated from that and implemented it for
unselected tabs (so trying to edit the AXValue is always going to select the
tab). I'm not sure if that makes sense though, so let me know if you think we
should copy Cocoa and just not allow AXValue of tabs to be editable / wait for
Views NSAccessibility actions.

As for AX_STATE_PRESSED, I think it's only for when the mouse is depressed on a
button and hasn't mouse upped yet. And AX_STATE_DISABLED is set by
NativeViewAccessibility::GetData() :D

+
 void Tab::OnFocus() {
   OnStateChanged();
   // When the tab gains focus, send an accessibility event indicating that the