Switch SupportsUserData uses to use unique_ptr.

ios/chrome/browser/web/dom_altering_lock.h

 // 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.
 
 #ifndef IOS_CHROME_BROWSER_WEB_DOM_ALTERING_LOCK_H_
 #define IOS_CHROME_BROWSER_WEB_DOM_ALTERING_LOCK_H_
 
 #include "base/ios/block_types.h"
 #import "base/ios/weak_nsobject.h"
 #include "ios/web/public/web_state/web_state_user_data.h"
@@ skipping 23 matching lines @@
 // Method called when another class wants to acquire the lock.
 // The class must restore the DOM tree, call DOMAlteringLock::Release() and then
 // |completionHandler|.
 - (void)releaseDOMLockWithCompletionHandler:(ProceduralBlock)completionHandler;
 
 @end
 
 class DOMAlteringLock : public web::WebStateUserData<DOMAlteringLock> {
  public:
   DOMAlteringLock(web::WebState* web_state);
+  ~DOMAlteringLock() override;
 
   // This method must be called before altering the DOM of the page. This will
   // ensure that only one class tries to alter the page at a time.
   // The completion handler is called with YES if the lock was acquired, or NO
   // if it could not.
   // This method must be called on the UI thread.
   void Acquire(id<DOMAltering> feature, ProceduralBlockWithBool lockAction);
 
   // Releases the lock on the DOM tree.
   // The lock is always released, even if it was acquired multiple times.
   // This method must be called on the UI thread.
   void Release(id<DOMAltering> feature);
 
  private:
   // DOMAltering object currently having the lock.
   base::WeakNSProtocol<id<DOMAltering>> current_dom_altering_feature_;
-
-  ~DOMAlteringLock() override;
 };
 
 #endif  // IOS_CHROME_BROWSER_WEB_DOM_ALTERING_LOCK_H_