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..221ef764dbcb51613de8b7644233b4234256ff93 100644
--- a/ui/accessibility/platform/ax_platform_node_mac.mm
+++ b/ui/accessibility/platform/ax_platform_node_mac.mm
@@ -12,7 +12,9 @@
 #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"
+#include "ui/strings/grit/ui_strings.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 +381,13 @@ void NotifyMacEvent(AXPlatformNodeCocoa* target, ui::AXEvent event_type) {
     return NO;
   }
 
+  // Since tabs use the Radio Button role on Mac, the standard way to set them
+  // is via the value attribute rather than the selected attribute.
+  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 +408,9 @@ 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;
+      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 +479,14 @@ void NotifyMacEvent(AXPlatformNodeCocoa* target, ui::AXEvent event_type) {
 }
 
 - (NSString*)AXRoleDescription {
+  switch (node_->GetData().role) {
+    case ui::AX_ROLE_TAB:
+      // There is no NSAccessibilityTabRole or similar (AXRadioButton is used
+      // instead). Do the same as NSTabView and put "tab" in the description.
+      return [l10n_util::GetNSStringWithFixup(IDS_ACCNAME_TAB) lowercaseString];
+    default:
+      break;
+  }
   return NSAccessibilityRoleDescription([self AXRole], [self AXSubrole]);
 }
 
@@ -480,6 +499,8 @@ 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 +571,13 @@ void NotifyMacEvent(AXPlatformNodeCocoa* target, ui::AXEvent event_type) {
       valueWithRange:NSMakeRange(0, [[self AXNumberOfCharacters] intValue])];
 }
 
+// Misc NSAccessibility attributes.
+
+- (NSNumber*)AXSelected {
+  return [NSNumber
+      numberWithBool:node_->GetData().HasStateFlag(ui::AX_STATE_SELECTED)];
+}
+
 @end
 
 namespace ui {