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 db0258319ce14ea934ea95de8bf9efb534e836ed..9f1d3a70a5d339ddc924b6757a5be5f00831a268 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -70649,12 +70649,11 @@ 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>
 
@@ -108927,6 +108926,12 @@ 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)"/>