Omnibox Metrics - Record Clipboard URL Impressions

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 f43eb981874b423d8dea38d9955659475e0b5aec..3d5c9f204017d74a51d3c66278606a9dd9526860 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -44223,6 +44223,30 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Omnibox.ClipboardSuggestionShownWithCurrentURL"
+    enum="BooleanPresent">
+  <owner>mpearson@chromium.org</owner>
+  <summary>
+    Recorded every time the omnibox is focussed and a recent URL from the user's
+    clipboard is suggested.  The value indicates whether the current URL was
+    shown (which would appear above the clipboard URL suggestion) or was absent
+    (which ought to only happen when the omnibox is empty / the user is on the
+    NTP).
+
+    On Android, the total count for this histogram can be usefully compared with
+    the count of the user action FocusLocation in order to determine the rate at
+    which a clipboard URL suggestion is shown in the omnibox.  To determine the
+    same rate on iOS, one needs to compare this histogram's count with the sum
+    of the user actions MobileFocusedOmniboxOnNtp, MobileFocusedFakeboxOnNtp,
+    and MobileFocusedOmniboxNotOnNtp.

[Ilya Sherman, 2017/03/31 16:52:43]

I wouldn't normally recommend comparing histograms against user actions.  At
least in the past, we saw significant skew between them.  I'm not sure whether
that's 100% better now, even with Rob's changes around when we drop metrics.

[Mark P, 2017/03/31 16:54:42]

Good point.

That said, I sanity-checked using the counts of user actions and comparing them
to omnibox events, and the the ratio is right around what I'd expect.

[Ilya Sherman, 2017/03/31 16:56:05]

Okay.  As long as you're comfortable with that potential skew, LGTM.

+
+    Furthermore, on either platform, this histogram's count can be usefully
+    compared with the count in the clipboard bucket of the
+    Omnibox.SuggestionUsed.Provider histogram to determine the clickthrough rate
+    on these suggestions.
+  </summary>
+</histogram>
+
 <histogram name="Omnibox.CutOrCopyAllText" units="count">
   <owner>mpearson@chromium.org</owner>
   <summary>