Push API: Don't unsubscribe when finding Service Worker fails

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 765057bf1a826efaf038ddec1f4349aec05f0568..d108937f9b455e3c85810164c6e305d9517b5905 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -47465,8 +47465,28 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 <histogram name="PushMessaging.DeliveryStatus" enum="PushDeliveryStatus">
   <owner>johnme@google.com</owner>
   <summary>
-    When a Service Worker receives a push message, this records whether it was
-    successful, or otherwise the type of error encountered.
+    When a Service Worker receives a push message, this records whether the
+    overall operation was successful, or otherwise the type of error
+    encountered.
+  </summary>
+</histogram>
+
+<histogram name="PushMessaging.DeliveryStatus.FindServiceWorker"
+    enum="ServiceWorkerStatusCode">
+  <owner>johnme@google.com</owner>
+  <summary>
+    When attempting to deliver a push message to a Service Worker, this records
+    the result of finding the Service Worker registration given its ID and
+    origin.
+  </summary>
+</histogram>
+
+<histogram name="PushMessaging.DeliveryStatus.ServiceWorkerEvent"
+    enum="ServiceWorkerStatusCode">
+  <owner>johnme@google.com</owner>
+  <summary>
+    When a Service Worker receives a push message, this records the precise
+    result received from the Service Worker code.
   </summary>
 </histogram>