UKM: Added support for navigation sources

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 1c4d44452cc5eedec98d0cd66ee04273ec5dda27..5219357680d672bc5c43baf97199f96fdd21aa73 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -70290,6 +70290,23 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <summary>The status when loading UKM PersistedLogs from Prefs.</summary>
 </histogram>
 
+<histogram name="UKM.Sources.MaxSourcesHit" units="BooleanHit">
+  <owner>holte@chromium.org</owner>
+  <owner>rkaplow@chromium.org</owner>
+  <summary>
+    Counter for the number of times an UKM source was discarded due to the max
+    in-memory limit being hit.
+  </summary>
+</histogram>
+
+<histogram name="UKM.Sources.SerializedCount">
+  <owner>holte@chromium.org</owner>
+  <owner>rkaplow@chromium.org</owner>
+  <summary>
+    Counter for number of serialized UKM sources when storing a UKM log.
+  </summary>
+</histogram>
+
 <histogram name="UKM.UnsentLogs.DroppedSize" units="bytes">
   <owner>holte@chromium.org</owner>
   <owner>rkaplow@chromium.org</owner>