Adding previews information to PLM UKM

chrome/browser/previews/previews_infobar_delegate.h

 // Copyright 2016 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_PREVIEWS_PREVIEWS_INFOBAR_DELEGATE_H_
 #define CHROME_BROWSER_PREVIEWS_PREVIEWS_INFOBAR_DELEGATE_H_
 
 #include "base/callback.h"
 #include "base/strings/string16.h"
 #include "base/time/time.h"
@@ skipping 50 matching lines @@
       bool is_reload,
       const OnDismissPreviewsInfobarCallback& on_dismiss_callback);
 
   // ConfirmInfoBarDelegate overrides:
   int GetIconId() const override;
   base::string16 GetMessageText() const override;
   base::string16 GetLinkText() const override;
 
   base::string16 GetTimestampText() const;
 
+  // A key to identify opt out events.
+  static const void* OptOutEventKey();
+
  private:
   PreviewsInfoBarDelegate(
       PreviewsInfoBarTabHelper* infobar_tab_helper,
       previews::PreviewsType previews_type,
       base::Time previews_freshness,
       bool is_data_saver_user,
       bool is_reload,
       const OnDismissPreviewsInfobarCallback& on_dismiss_callback);
 
   // ConfirmInfoBarDelegate overrides:
@@ skipping 12 matching lines @@
   mutable PreviewsInfoBarAction infobar_dismissed_action_;
 
   const base::string16 message_text_;
 
   OnDismissPreviewsInfobarCallback on_dismiss_callback_;
 
   DISALLOW_COPY_AND_ASSIGN(PreviewsInfoBarDelegate);
 };
 
 #endif  // CHROME_BROWSER_PREVIEWS_PREVIEWS_INFOBAR_DELEGATE_H_