Small fixes for url_index_private_data.cc

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 1043e5631c3993d0e32a18ba3388cdb14f3014aa..8d9e9893ff93d84cfda8dc75bfa82ba1573031a6 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -40749,6 +40749,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Omnibox.HistoryIDSetFromWordsForked" units="ms">

[Mark P, 2016/11/30 22:57:59]

This name does not match the name you used in the code.

Also, I suggest a name that makes it obvious that this only applies to the
HistoryQuick part of the omnibox.  E.g., Omnibox.HistoryQuickHistoryID... or
Omnibox.HQPHistoryID...

+  <owner>mpearson@chromium.org</owner>
+  <summary>
+    Times URLIndexPrivateData::HistoryIDSetFromWords. Recorded every time
+    HistoryQuick provider works, which could happen multiple times on each

[Peter Kasting, 2016/11/30 21:39:50]

"works" is kind of vague.  It seems like a more precise description might be
good.

[Mark P, 2016/11/30 22:57:59]

I suggest a rewording (with extra detail), something like the following:
Times URLIndexPrivateData::HistoryIDSetFromWords(), which is called by the
omnibox's HistoryQuick provider.  URLIndexPrivateData::HistoryIDSetFromWords()
can be called multiple times per keystroke due to, for example, the cursor being
in the middle of the input string or SearchProvider's calls to Classify().

+    keystroke.
+  </summary>
+</histogram>
+
 <histogram name="Omnibox.InputType" enum="OmniboxInputType">
   <owner>mpearson@chromium.org</owner>
   <summary>