Fix lifetime problems in AXPlatformNodeCocoa.

ui/accessibility/platform/ax_platform_node_mac.mm

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "ui/accessibility/platform/ax_platform_node_mac.h"
 
 #import <Cocoa/Cocoa.h>
 #include <stddef.h>
 
 #include "base/macros.h"
@@ skipping 293 matching lines @@
 }
 
 - (NSString*)getAXValueAsString {
   id value = [self AXValue];
   return [value isKindOfClass:[NSString class]] ? value : nil;
 }
 
 // NSAccessibility informal protocol implementation.
 
 - (BOOL)accessibilityIsIgnored {
+  if (!node_)
+    return YES;
+
   return [[self AXRole] isEqualToString:NSAccessibilityUnknownRole] ||
          node_->GetData().HasState(ui::AX_STATE_INVISIBLE);
 }
 
 - (id)accessibilityHitTest:(NSPoint)point {
   for (AXPlatformNodeCocoa* child in [self AXChildren]) {
     if (![child accessibilityIsIgnored] &&
         NSPointInRect(point, child.boundsInScreen)) {
       return [child accessibilityHitTest:point];
     }
   }
   return NSAccessibilityUnignoredAncestor(self);
 }
 
 - (BOOL)accessibilityNotifiesWhenDestroyed {
   return YES;
 }
 
 - (id)accessibilityFocusedUIElement {
-  return node_->GetDelegate()->GetFocus();
+  return node_ ? node_->GetDelegate()->GetFocus() : nil;
 }
 
 - (NSArray*)accessibilityActionNames {
+  if (!node_)
+    return @[];
+
   base::scoped_nsobject<NSMutableArray> axActions(
       [[NSMutableArray alloc] init]);
 
   const ui::AXNodeData& data = node_->GetData();
   const ActionList& action_list = GetActionList();
 
   // VoiceOver expects the "press" action to be first. Note that some roles
   // should be given a press action implicitly.
   DCHECK([action_list[0].second isEqualToString:NSAccessibilityPressAction]);
   for (const auto item : action_list) {
     if (data.HasAction(item.first) || HasImplicitAction(data, item.first))
       [axActions addObject:item.second];
   }
 
   if (AlsoUseShowMenuActionForDefaultAction(data))
     [axActions addObject:NSAccessibilityShowMenuAction];
 
   return axActions.autorelease();
 }
 
 - (void)accessibilityPerformAction:(NSString*)action {
-  DCHECK([[self accessibilityActionNames] containsObject:action]);
+  // Actions are performed asynchronously, so it's always possible for an object
+  // to change its mind after previously reporting an action as available.
+  if (![[self accessibilityActionNames] containsObject:action])
+    return;
+
   ui::AXActionData data;
   if ([action isEqualToString:NSAccessibilityShowMenuAction] &&
       AlsoUseShowMenuActionForDefaultAction(node_->GetData())) {
     data.action = ui::AX_ACTION_DO_DEFAULT;
   } else {
     for (const ActionList::value_type& entry : GetActionList()) {
       if ([action isEqualToString:entry.second]) {
         data.action = entry.first;
         break;
       }
     }
   }
 
   // Note ui::AX_ACTIONs which are just overwriting an accessibility attribute
   // are already implemented in -accessibilitySetValue:forAttribute:, so ignore
   // those here.
 
   if (data.action != ui::AX_ACTION_NONE)
     node_->GetDelegate()->AccessibilityPerformAction(data);
 }
 
 - (NSArray*)accessibilityAttributeNames {
+  if (!node_)
+    return @[];
+
   // These attributes are required on all accessibility objects.
   NSArray* const kAllRoleAttributes = @[
     NSAccessibilityChildrenAttribute,
     NSAccessibilityParentAttribute,
     NSAccessibilityPositionAttribute,
     NSAccessibilityRoleAttribute,
     NSAccessibilitySizeAttribute,
     NSAccessibilitySubroleAttribute,
 
     // Title is required for most elements. Cocoa asks for the value even if it
@@ skipping 49 matching lines @@
       break;
     // TODO(tapted): Add additional attributes based on role.
     default:
       break;
   }
   return axAttributes.autorelease();
 }
 
 - (NSArray*)accessibilityParameterizedAttributeNames {
   if (!node_)
-    return nil;
+    return @[];
 
   static NSArray* const kSelectableTextAttributes = [@[
     NSAccessibilityLineForIndexParameterizedAttribute,
     NSAccessibilityRangeForLineParameterizedAttribute,
     NSAccessibilityStringForRangeParameterizedAttribute,
     NSAccessibilityRangeForPositionParameterizedAttribute,
     NSAccessibilityRangeForIndexParameterizedAttribute,
     NSAccessibilityBoundsForRangeParameterizedAttribute,
     NSAccessibilityRTFForRangeParameterizedAttribute,
     NSAccessibilityStyleRangeForIndexParameterizedAttribute,
     NSAccessibilityAttributedStringForRangeParameterizedAttribute,
   ] retain];
 
   switch (node_->GetData().role) {
     case ui::AX_ROLE_TEXT_FIELD:
     case ui::AX_ROLE_STATIC_TEXT:
       return kSelectableTextAttributes;
     default:
       break;
   }
   return nil;
 }
 
 - (BOOL)accessibilityIsAttributeSettable:(NSString*)attributeName {
+  if (!node_)
+    return NO;
+
   if (node_->GetData().HasState(ui::AX_STATE_DISABLED))
     return NO;
 
   // 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:NSAccessibilitySelectedChildrenAttribute] ||
       [attributeName
           isEqualToString:NSAccessibilityVisibleCharacterRangeAttribute]) {
@@ skipping 17 matching lines @@
   if ([attributeName isEqualToString:NSAccessibilityFocusedAttribute]) {
     return node_->GetData().HasState(ui::AX_STATE_FOCUSABLE);
   }
 
   // TODO(patricialor): Add callbacks for updating the above attributes except
   // NSAccessibilityValueAttribute and return YES.
   return NO;
 }
 
 - (void)accessibilitySetValue:(id)value forAttribute:(NSString*)attribute {
+  if (!node_)
+    return;
+
   ui::AXActionData data;
 
   // Check for attributes first. Only the |data.action| should be set here - any
   // type-specific information, if needed, should be set below.
   if ([attribute isEqualToString:NSAccessibilityValueAttribute]) {
     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;
@@ skipping 18 matching lines @@
   }
 
   if (data.action != ui::AX_ACTION_NONE)
     node_->GetDelegate()->AccessibilityPerformAction(data);
 
   // TODO(patricialor): Plumb through all the other writable attributes as
   // specified in accessibilityIsAttributeSettable.
 }
 
 - (id)accessibilityAttributeValue:(NSString*)attribute {
+  if (!node_)
+    return nil;  // Return nil when detached. Even for AXRole.
+
   SEL selector = NSSelectorFromString(attribute);
   if ([self respondsToSelector:selector])
     return [self performSelector:selector];
   return nil;
 }
 
 - (id)accessibilityAttributeValue:(NSString*)attribute
                      forParameter:(id)parameter {
+  if (!node_)
+    return nil;
+
   SEL selector = NSSelectorFromString([attribute stringByAppendingString:@":"]);
   if ([self respondsToSelector:selector])
     return [self performSelector:selector withObject:parameter];
   return nil;
 }
 
 // NSAccessibility attributes. Order them according to
 // NSAccessibilityConstants.h, or see https://crbug.com/678898.
 
 - (NSString*)AXRole {
   if (!node_)
     return nil;
+
   return [[self class] nativeRoleFromAXRole:node_->GetData().role];
 }
 
 - (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_ROLE_DESCRIPTION)
           lowercaseString];
@@ skipping 47 matching lines @@
 }
 
 - (id)AXParent {
   if (!node_)
     return nil;
   return NSAccessibilityUnignoredAncestor(node_->GetParent());
 }
 
 - (NSArray*)AXChildren {
   if (!node_)
-    return nil;
+    return @[];
+
   int count = node_->GetChildCount();
   NSMutableArray* children = [NSMutableArray arrayWithCapacity:count];
   for (int i = 0; i < count; ++i)
     [children addObject:node_->ChildAtIndex(i)];
   return NSAccessibilityUnignoredChildren(children);
 }
 
 - (id)AXWindow {
   return node_->GetDelegate()->GetTopLevelWidget();
 }
@@ skipping 172 matching lines @@
   }
   NotifyMacEvent(native_node_, event_type);
 }
 
 int AXPlatformNodeMac::GetIndexInParent() {
   // TODO(dmazzoni): implement this.  http://crbug.com/396137
   return -1;
 }
 
 }  // namespace ui