Make WeakContainer safe when weak_nsobject.h is included from ARC code.

base/ios/weak_nsobject.h

 // Copyright 2013 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 BASE_IOS_WEAK_NSOBJECT_H_
 #define BASE_IOS_WEAK_NSOBJECT_H_
 
 #import <Foundation/Foundation.h>
 #import <objc/runtime.h>
 
@@ skipping 31 matching lines @@
 //       that copy must return to the original thread before being dereferenced,
 //   (2) it is allowed to destroy a WeakNSObject on any thread;
 // - the implementation assumes that the tracked object will be released on the
 //   same thread that the WeakNSObject is created on.
 namespace base {
 
 // WeakContainer keeps a weak pointer to an object and clears it when it
 // receives nullify() from the object's sentinel.
 class WeakContainer : public base::RefCountedThreadSafe<WeakContainer> {
  public:
-  explicit WeakContainer(id object) : object_(object) {}
+  explicit WeakContainer(id object);
 
   id object() {
     DCHECK(checker_.CalledOnValidThread());
     return object_;
   }
 
   void nullify() {
     DCHECK(checker_.CalledOnValidThread());
     object_ = nil;
   }
 
  private:
   friend base::RefCountedThreadSafe<WeakContainer>;
-  ~WeakContainer() {}
+  ~WeakContainer();
   base::ThreadChecker checker_;
-  id object_;
+  __unsafe_unretained id object_;
 };
 
 }  // namespace base
 
 // Sentinel for observing the object contained in the weak pointer. The object
 // will be deleted when the weak object is deleted and will notify its
 // container.
 @interface CRBWeakNSProtocolSentinel : NSObject
 // Return the only associated container for this object. There can be only one.
 // Will return null if object is nil .
@@ skipping 99 matching lines @@
 
   WeakNSObject& operator=(const WeakNSObject<id>& that) {
     WeakNSProtocol<id>::operator=(that);
     return *this;
   }
 };
 
 }  // namespace base
 
 #endif  // BASE_IOS_WEAK_NSOBJECT_H_