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 262 matching lines @@
   node_ = nil;
 }
 
 - (NSRect)boundsInScreen {
   if (!node_)
     return NSZeroRect;
   return gfx::ScreenRectToNSRect(node_->GetBoundsInScreen());
 }
 
 - (NSString*)getStringAttribute:(ui::AXStringAttribute)attribute {
+  if (!node_)

[dmazzoni, 2017/06/20 17:47:16]

Isn't this an internal helper method? It seems like it
shouldn't be necessary to check at the top of every method,
only at the top of public APIs (below where it says
"NSAccessibility informal protocol implementation".

[tapted, 2017/06/20 23:30:52]

Removed - I think this was just left over from earlier iterations.

+    return nil;
+
   std::string attributeValue;
   if (node_->GetStringAttribute(attribute, &attributeValue))
     return base::SysUTF8ToNSString(attributeValue);
   return nil;
 }
 
 - (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();
 
   // VoiceOver expects the "press" action to be first.
   if (ui::IsRoleClickable(data.role) || data.HasAction(kActionForPress))
     [axActions addObject:NSAccessibilityPressAction];
 
   for (const ActionMap::value_type& entry : GetActionMap()) {
     if (entry.first == kActionForPress)
       continue;
 
     DCHECK(![entry.second isEqualToString:NSAccessibilityPressAction]);
 
     if (data.HasAction(entry.first))
       [axActions addObject:entry.second];
   }
 
   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;
   for (const ActionMap::value_type& entry : GetActionMap()) {
     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 48 matching lines @@
       [axAttributes addObjectsFromArray:kValueAttributes];
       break;
     // TODO(tapted): Add additional attributes based on role.
     default:
       break;
   }
   return axAttributes.autorelease();
 }
 
 - (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;
 }
 
 // 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 44 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 109 matching lines @@
   }
   NotifyMacEvent(native_node_, event_type);
 }
 
 int AXPlatformNodeMac::GetIndexInParent() {
   // TODO(dmazzoni): implement this.  http://crbug.com/396137
   return -1;
 }
 
 }  // namespace ui