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

ui/accessibility/platform/ax_platform_node_mac.mm

Index: ui/accessibility/platform/ax_platform_node_mac.mm
diff --git a/ui/accessibility/platform/ax_platform_node_mac.mm b/ui/accessibility/platform/ax_platform_node_mac.mm
index b06cb439dfc32467381b54aaa1d3a25868ed1589..b0e906706875eb55a873c9a65bfb78488eb1c309 100644
--- a/ui/accessibility/platform/ax_platform_node_mac.mm
+++ b/ui/accessibility/platform/ax_platform_node_mac.mm
@@ -9,9 +9,11 @@
 
 #include "base/macros.h"
 #include "base/strings/sys_string_conversions.h"
+#include "chrome/grit/generated_resources.h"
 #include "ui/accessibility/ax_action_data.h"
 #include "ui/accessibility/ax_node_data.h"
 #include "ui/accessibility/platform/ax_platform_node_delegate.h"
+#include "ui/base/l10n/l10n_util.h"
 #import "ui/gfx/mac/coordinate_conversion.h"
 
 namespace {
@@ -184,6 +186,7 @@ RoleMap BuildSubroleMap() {
       {ui::AX_ROLE_SEARCH_BOX, @"AXSearchField"},
       {ui::AX_ROLE_STATUS, @"AXApplicationStatus"},
       {ui::AX_ROLE_SWITCH, @"AXSwitch"},
+      {ui::AX_ROLE_TAB, @"AXTab"},
       {ui::AX_ROLE_TAB_PANEL, @"AXTabPanel"},
       {ui::AX_ROLE_TIMER, @"AXApplicationTimer"},
       {ui::AX_ROLE_TOGGLE_BUTTON, @"AXToggleButton"},
@@ -369,8 +372,7 @@ void NotifyMacEvent(AXPlatformNodeCocoa* target, ui::AXEvent event_type) {
   // Allow certain attributes to be written via an accessibility client. A
   // writable attribute will only appear as such if the accessibility element
   // has a value set for that attribute.
-  if ([attributeName isEqualToString:NSAccessibilitySelectedAttribute] ||
-      [attributeName
+  if ([attributeName
           isEqualToString:NSAccessibilitySelectedChildrenAttribute] ||
       [attributeName
           isEqualToString:NSAccessibilitySelectedTextRangeAttribute] ||
@@ -379,6 +381,14 @@ void NotifyMacEvent(AXPlatformNodeCocoa* target, ui::AXEvent event_type) {
     return NO;
   }
 
+  // Tabs are a special case. For whatever reason,

[tapted, 2017/01/03 00:29:27]

The reason might be that in Cocoa, using role=AXRadioButton for NSTabView and
NSSegmentedControl is a bit of a "hack". E.g. "value" maps logically to a radio
button, but not so much to a tab. If I understand correctly, I think we can
mention that. I.e. "Since tabs use the Radio Button role on Mac, the standard
way to set them is via the value attributed rather than the selected attribute".

[Patti Lor, 2017/01/06 02:02:29]

Done.

+  // NSAccessibilitySelectedAttribute isn't used for them, so allow editing of
+  // the value attribute to select unselected tabs instead.
+  if ([attributeName isEqualToString:NSAccessibilityValueAttribute] &&
+      node_->GetData().role == ui::AX_ROLE_TAB) {
+    return !node_->GetData().HasStateFlag(ui::AX_STATE_SELECTED);
+  }
+
   if ([attributeName isEqualToString:NSAccessibilityValueAttribute] ||
       [attributeName isEqualToString:NSAccessibilitySelectedTextAttribute])
     return !ui::AXNodeData::IsFlagSet(node_->GetData().state,
@@ -399,7 +409,11 @@ void NotifyMacEvent(AXPlatformNodeCocoa* target, ui::AXEvent event_type) {
   if ([value isKindOfClass:[NSString class]]) {
     data.value = base::SysNSStringToUTF16(value);
     if ([attribute isEqualToString:NSAccessibilityValueAttribute]) {
-      data.action = ui::AX_ACTION_SET_VALUE;
+      // Tabs have no other way to set their selected state via a11y, so use the
+      // value attribute here.
+      data.action = node_->GetData().role == ui::AX_ROLE_TAB
+                        ? ui::AX_ACTION_SET_SELECTION
+                        : ui::AX_ACTION_SET_VALUE;
     } else if ([attribute
                    isEqualToString:NSAccessibilitySelectedTextAttribute]) {
       data.action = ui::AX_ACTION_REPLACE_SELECTED_TEXT;
@@ -468,6 +482,13 @@ void NotifyMacEvent(AXPlatformNodeCocoa* target, ui::AXEvent event_type) {
 }
 
 - (NSString*)AXRoleDescription {
+  ui::AXRole role = node_->GetData().role;
+  switch (role) {

[tapted, 2017/01/03 00:29:27]

nit: switch (node_->GetData().role) {

[Patti Lor, 2017/01/06 02:02:29]

Done.

+    case ui::AX_ROLE_TAB:
+      return l10n_util::GetNSStringWithFixup(IDS_ACCNAME_TAB);

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

There's no "NSAccessibilityTabRole" or similar, so using the same approach as
chrome/browser/ui/cocoa/tabs/tab_view.mm and setting role description manually.

[tapted, 2017/01/03 00:29:27]

Can we move IDS_ACCNAME_TAB to ui_resources.grd? I think that will fix the
layering stuff. Also can we add a note to the case e.g.

    // There is no NSAccessibilityTabRole or similar (AXRadioButton is used
instead). Do the same as NSTabView and put "tab" in the description.

(that's assuming what I said there is correct :)

[Patti Lor, 2017/01/06 02:02:29]

A recent patch (https://codereview.chromium.org/2518183002) conveniently added
ui/strings/ui_strings.h to ui/accessibility/DEPS, so I moved it there instead,
hopefully that's OK :)

+    default:
+      break;
+  }
   return NSAccessibilityRoleDescription([self AXRole], [self AXSubrole]);
 }
 
@@ -480,6 +501,8 @@ void NotifyMacEvent(AXPlatformNodeCocoa* target, ui::AXEvent event_type) {
 }
 
 - (NSString*)AXValue {
+  if (node_->GetData().role == ui::AX_ROLE_TAB)
+    return [[self AXSelected] stringValue];
   return [self getStringAttribute:ui::AX_ATTR_VALUE];
 }
 
@@ -550,6 +573,13 @@ void NotifyMacEvent(AXPlatformNodeCocoa* target, ui::AXEvent event_type) {
       valueWithRange:NSMakeRange(0, [[self AXNumberOfCharacters] intValue])];
 }
 
+// Misc NSAccessibility attributes.
+
+- (NSNumber*)AXSelected {

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

Not sure if we should leave this in; I can't tell if it does anything. It is
definitely called, though. WDYT?

[tapted, 2017/01/03 00:29:27]

This looks good.  I think it's fine to add anything from AXAttributeConstants.h

[Patti Lor, 2017/01/06 02:02:29]

Acknowledged.

+  return [NSNumber
+      numberWithBool:node_->GetData().HasStateFlag(ui::AX_STATE_SELECTED)];
+}
+
 @end
 
 namespace ui {