[Mac] Use object_destructInstance() if available.

chrome/browser/ui/cocoa/objc_zombie.h

 // Copyright (c) 2010 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.
 
 #ifndef CHROME_BROWSER_UI_COCOA_NSOBJECT_ZOMBIE_H_
 #define CHROME_BROWSER_UI_COCOA_NSOBJECT_ZOMBIE_H_
 #pragma once
 
 #import <Foundation/Foundation.h>
 
 // You should think twice every single time you use anything from this
 // namespace.
 namespace ObjcEvilDoers {
 
+// Which version of the runtime to expect when initializing.  This
+// decision is left to the caller so that unit tests and production
+// uses can make different decisions.
+enum Runtime {
+  RUNTIME_GUESS,

[Mark Mentovai, 2011/06/07 21:42:57]

This is only used in test code. Seems like you duplicate the OS-version
detection for the same purpose in two locations, once in
chrome_browser_application.mm (used in production) and once in objc_zombie.mm
(used by RUNTIME_GUESS in tests). Not so hot.

What if you left all of the detective work in objc_zombie.mm and had the
zombie-setup code return a value that indicates success, failed-10.5,
failed-10.6, failed-otherwise?

[Scott Hess - ex-Googler, 2011/06/07 23:48:21]

RUNTIME_10_x is for the specific runtime, while RUNTIME_GUESS tries for 10.6,
and if it fails tries for 10.5.
I'm having some brain mismatch in here.  For some reason I feel like the
zombie-setup code is more basic stuff that should provide capabilities but not
make policy decisions.  So it knows "This function is present via dlsym(), so we
work in this case", but if that function is _not_ present, should that mean we
have the wrong version, or that we should fallback to the older version?

+  RUNTIME_10_5,
+  RUNTIME_10_6,
+};
+
 // Enable zombie object debugging. This implements a variant of Apple's
 // NSZombieEnabled which can help expose use-after-free errors where messages
 // are sent to freed Objective-C objects in production builds.
 //
 // Returns NO if it fails to enable.
 //
 // When |zombieAllObjects| is YES, all objects inheriting from
 // NSObject become zombies on -dealloc.  If NO, -shouldBecomeCrZombie
 // is queried to determine whether to make the object a zombie.
 //
 // |zombieCount| controls how many zombies to store before freeing the
 // oldest.  Set to 0 to free objects immediately after making them
 // zombies.
-BOOL ZombieEnable(BOOL zombieAllObjects, size_t zombieCount);
+BOOL ZombieEnable(Runtime runtime, BOOL zombieAllObjects, size_t zombieCount);
 
 // Disable zombies.
 void ZombieDisable();
 
 }  // namespace ObjcEvilDoers
 
 @interface NSObject (CrZombie)
 - (BOOL)shouldBecomeCrZombie;
 @end
 
 #endif  // CHROME_BROWSER_UI_COCOA_NSOBJECT_ZOMBIE_H_