Change the logic for discarding all non-histogram logs because of actions/omnibox events to truncat…

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 6ed192b3a430a9c42cd098e58111a7082c27aa59..ead00624f8553093baf3e633dd35b0cf4d2fe018 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -77719,6 +77719,9 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 </histogram>
 
 <histogram name="UMA.Discarded Log Events">
+  <obsolete>
+    Replaced by UMA.Truncate* metrics.
+  </obsolete>
   <owner>asvitkine@chromium.org</owner>
   <owner>rkaplow@chromium.org</owner>
   <summary>
@@ -78209,6 +78212,22 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="UMA.TruncatedEvents.Omnibox" units="events">
+  <owner>rkaplow@chromium.org</owner>
+  <summary>
+    The number of omnibox events that existed in the metrics log before we
+    truncated them to save bandwidth.
+  </summary>
+</histogram>
+
+<histogram name="UMA.TruncatedEvents.UserAction" units="events">
+  <owner>rkaplow@chromium.org</owner>
+  <summary>
+    The number of user actions events that existed in the metrics log before we
+    truncated them to save bandwidth.
+  </summary>
+</histogram>
+
 <histogram name="UMA.Unacceptable_Log_Discarded">
   <obsolete>
     Deprecated as of May, 2012 (i.e. Chrome 21+).  Replaced by the