UMA for the Stale Previews timestamp

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 2066ab170e99b48ffbc46b490a0439b07c9b7ca5..da94bd2ea8137ebb6d64c02d9a7b72c77fccd5e0 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -58017,6 +58017,14 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Previews.InfoBarTimestamp" enum="PreviewsInfoBarTimestamp">
+  <owner>megjablon@chromium.org</owner>
+  <summary>
+    Whether the timestamp for a stale preview was shown on the infobar. If the
+    timestamp was not shown, states the reason why.
+  </summary>
+</histogram>
+
 <histogram name="Previews.OptOut.DBRowCount" units="rows">
   <owner>ryansturm@chromium.org</owner>
   <summary>
@@ -65613,8 +65621,8 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <summary>
     Time between starting raster work on the pending tree and when it is ready
     to activate. Unlike PendingTreeDuration which - includes the time to commit
-    to this tree, the raster duration and the time for which the pending
-    tree waits before it can be activated - this only measures the time taken to
+    to this tree, the raster duration and the time for which the pending tree
+    waits before it can be activated - this only measures the time taken to
     rasterize tiles required for activation.
 
     The interval is recorded each time we are notifed that a pending tree is