Switch SupportsUserData uses to use unique_ptr.

ios/chrome/browser/infobars/infobar_manager_impl.h

Index: ios/chrome/browser/infobars/infobar_manager_impl.h
diff --git a/ios/chrome/browser/infobars/infobar_manager_impl.h b/ios/chrome/browser/infobars/infobar_manager_impl.h
index 648b8cb737b0fd18ef0ed9a2b91b81b0cf8040ff..e445dd18fb2471e508acc7f429de86b12172940d 100644
--- a/ios/chrome/browser/infobars/infobar_manager_impl.h
+++ b/ios/chrome/browser/infobars/infobar_manager_impl.h
@@ -27,6 +27,8 @@ class InfoBarManagerImpl : public infobars::InfoBarManager,
                            public web::WebStateObserver,
                            public web::WebStateUserData<InfoBarManagerImpl> {
  public:
+  ~InfoBarManagerImpl() override;
+
   // This function must only be called on infobars that are owned by an
   // InfoBarManagerImpl instance (or not owned at all, in which case this
   // returns null).
@@ -36,7 +38,6 @@ class InfoBarManagerImpl : public infobars::InfoBarManager,
   friend class web::WebStateUserData<InfoBarManagerImpl>;
 
   explicit InfoBarManagerImpl(web::WebState* web_state);
-  ~InfoBarManagerImpl() override;
 
   // InfoBarManager implementation.
   int GetActiveEntryID() override;