UKM Sync Observer

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 616abde71e0a7d4efbecf5e45630c57ab9be3401..89b9e0aa5c691dc0bb0f1a11eeaceae73b075464 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -70897,12 +70897,11 @@ 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">
+<histogram name="UKM.Sources.Dropped" enum="UkmSourceDroppedReason">
   <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.
+    Counters for the rate at which UKM Sources are dropped for various reasons.
   </summary>
 </histogram>
 
@@ -109357,6 +109356,12 @@ value.
   <int value="36" label="Tap unconfirmed"/>
 </enum>
 
+<enum name="UkmSourceDroppedReason" type="int">
+  <int value="0" label="Not dropped"/>
+  <int value="1" label="Recording disabled"/>
+  <int value="2" label="Max sources hit"/>
+</enum>
+
 <enum name="UmaCleanExitConsistency" type="int">
   <int value="0" label="Dirty/Dirty (Registry/Local State)"/>
   <int value="1" label="Dirty/Clean (Registry/Local State)"/>