Revert of Fix lifetime problems in AXPlatformNodeCocoa.

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 2b09d34d70eab2b78d19fb0bffa5eba1d8576ac4..2eb4dba0a3ac50dff8940613b19157feedcb0654 100644
--- a/ui/accessibility/platform/ax_platform_node_mac.mm
+++ b/ui/accessibility/platform/ax_platform_node_mac.mm
@@ -311,9 +311,6 @@
 // NSAccessibility informal protocol implementation.
 
 - (BOOL)accessibilityIsIgnored {
-  if (!node_)
-    return YES;
-
   return [[self AXRole] isEqualToString:NSAccessibilityUnknownRole] ||
          node_->GetData().HasState(ui::AX_STATE_INVISIBLE);
 }
@@ -333,13 +330,10 @@
 }
 
 - (id)accessibilityFocusedUIElement {
-  return node_ ? node_->GetDelegate()->GetFocus() : nil;
+  return node_->GetDelegate()->GetFocus();
 }
 
 - (NSArray*)accessibilityActionNames {
-  if (!node_)
-    return @[];
-
   base::scoped_nsobject<NSMutableArray> axActions(
       [[NSMutableArray alloc] init]);
 
@@ -361,11 +355,7 @@
 }
 
 - (void)accessibilityPerformAction:(NSString*)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;
-
+  DCHECK([[self accessibilityActionNames] containsObject:action]);
   ui::AXActionData data;
   if ([action isEqualToString:NSAccessibilityShowMenuAction] &&
       AlsoUseShowMenuActionForDefaultAction(node_->GetData())) {
@@ -388,9 +378,6 @@
 }
 
 - (NSArray*)accessibilityAttributeNames {
-  if (!node_)
-    return @[];
-
   // These attributes are required on all accessibility objects.
   NSArray* const kAllRoleAttributes = @[
     NSAccessibilityChildrenAttribute,
@@ -460,7 +447,7 @@
 
 - (NSArray*)accessibilityParameterizedAttributeNames {
   if (!node_)
-    return @[];
+    return nil;
 
   static NSArray* const kSelectableTextAttributes = [@[
     NSAccessibilityLineForIndexParameterizedAttribute,
@@ -485,9 +472,6 @@
 }
 
 - (BOOL)accessibilityIsAttributeSettable:(NSString*)attributeName {
-  if (!node_)
-    return NO;
-
   if (node_->GetData().HasState(ui::AX_STATE_DISABLED))
     return NO;
 
@@ -525,9 +509,6 @@
 }
 
 - (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
@@ -566,9 +547,6 @@
 }
 
 - (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];
@@ -577,9 +555,6 @@
 
 - (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];
@@ -592,7 +567,6 @@
 - (NSString*)AXRole {
   if (!node_)
     return nil;
-
   return [[self class] nativeRoleFromAXRole:node_->GetData().role];
 }
 
@@ -660,8 +634,7 @@
 
 - (NSArray*)AXChildren {
   if (!node_)
-    return @[];
-
+    return nil;
   int count = node_->GetChildCount();
   NSMutableArray* children = [NSMutableArray arrayWithCapacity:count];
   for (int i = 0; i < count; ++i)