Track Previews infobar dismissals due to tab closure

chrome/browser/previews/previews_infobar_delegate.h

Index: chrome/browser/previews/previews_infobar_delegate.h
diff --git a/chrome/browser/previews/previews_infobar_delegate.h b/chrome/browser/previews/previews_infobar_delegate.h
index cc35b24bd614e54eb96743b107a7609a0af19ed0..f362be5c2a58d71a574dda0d2228860e1cc085b7 100644
--- a/chrome/browser/previews/previews_infobar_delegate.h
+++ b/chrome/browser/previews/previews_infobar_delegate.h
@@ -37,6 +37,7 @@ class PreviewsInfoBarDelegate : public ConfirmInfoBarDelegate {
     INFOBAR_DISMISSED_BY_USER = 2,
     INFOBAR_DISMISSED_BY_NAVIGATION = 3,
     INFOBAR_DISMISSED_BY_RELOAD = 4,
+    INFOBAR_DISMISSED_BY_TAB_CLOSURE = 5,
     INFOBAR_INDEX_BOUNDARY
   };
 
@@ -68,6 +69,7 @@ class PreviewsInfoBarDelegate : public ConfirmInfoBarDelegate {
   bool LinkClicked(WindowOpenDisposition disposition) override;
 
   PreviewsInfoBarType infobar_type_;
+  mutable PreviewsInfoBarAction infobar_dismissed_action_;
 
   const base::string16 message_text_;