UMA for the Stale Previews timestamp

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 17 matching lines @@
   enum PreviewsInfoBarAction {
     INFOBAR_SHOWN = 0,
     INFOBAR_LOAD_ORIGINAL_CLICKED = 1,
     INFOBAR_DISMISSED_BY_USER = 2,
     INFOBAR_DISMISSED_BY_NAVIGATION = 3,
     INFOBAR_DISMISSED_BY_RELOAD = 4,
     INFOBAR_DISMISSED_BY_TAB_CLOSURE = 5,
     INFOBAR_INDEX_BOUNDARY
   };
 
+  // Values of the UMA Previews.InfoBarTimestamp histogram. This enum must
+  // remain synchronized with the enum of the same name in
+  // metrics/histograms/histograms.xml.
+  enum PreviewsInfoBarTimestamp {
+    TIMESTAMP_SHOWN = 0,
+    TIMESTAMP_NOT_SHOWN_PREVIEW_NOT_STALE = 1,
+    TIMESTAMP_NOT_SHOWN_STALENESS_NEGATIVE = 2,
+    TIMESTAMP_NOT_SHOWN_STALENESS_GREATER_THAN_MAX = 3,
+    TIMESTAMP_INDEX_BOUNDARY
+  };
+
   ~PreviewsInfoBarDelegate() override;
 
   // Creates a preview infobar and corresponding delegate and adds the infobar
   // to InfoBarService.
   static void Create(
       content::WebContents* web_contents,
       previews::PreviewsType previews_type,
       base::Time previews_freshness,
       bool is_data_saver_user,
       const OnDismissPreviewsInfobarCallback& on_dismiss_callback);
@@ skipping 27 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_