service worker: Attribute purpose to start worker attempts for UMA

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 a5fa0356a81177921932dcf9a650fc84454cfdba..60140b3367e41a614910052a1d7bdff63781a7fb 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -45951,6 +45951,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="ServiceWorker.StartWorker.Purpose"
+    enum="ServiceWorkerMetrics.EventType">
+  <owner>falken@chromium.org</owner>
+  <summary>
+    The purpose for starting up a service worker. Recorded only for installed
+    workers.
+  </summary>
+</histogram>
+
 <histogram name="ServiceWorker.StartWorker.Status"
     enum="ServiceWorkerStatusCode">
   <owner>falken@chromium.org</owner>
@@ -45971,6 +45980,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="ServiceWorker.StartWorker.Timeout.StartPurpose"
+    enum="ServiceWorkerMetrics.EventType">
+  <owner>falken@chromium.org</owner>
+  <summary>
+    Records the start purpose for a service worker that timed out while starting
+    up. Recorded only for installed workers.
+  </summary>
+</histogram>
+
 <histogram name="ServiceWorker.StartWorker.TimeoutPhase"
     enum="EmbeddedWorkerStartingPhase">
   <owner>falken@chromium.org</owner>
@@ -80171,13 +80189,19 @@ To add a new entry, add it with any value and run test to compute valid value.
 <enum name="ServiceWorkerMetrics.EventType" type="int">
   <int value="0" label="ACTIVATE"/>
   <int value="1" label="INSTALL"/>
-  <int value="2" label="FETCH"/>
+  <int value="2" label="FETCH (deprecated)"/>
   <int value="3" label="SYNC"/>
   <int value="4" label="NOTIFICATION_CLICK"/>
   <int value="5" label="PUSH"/>
   <int value="6" label="GEOFENCING"/>
   <int value="7" label="SERVICE_PORT_CONNECT"/>
   <int value="8" label="MESSAGE"/>
+  <int value="9" label="NOTIFICATION_CLOSE"/>
+  <int value="10" label="FETCH_MAIN_FRAME"/>
+  <int value="11" label="FETCH_SUB_FRAME"/>
+  <int value="12" label="FETCH_SHARED_WORKER"/>
+  <int value="13" label="FETCH_SUB_RESOURCE"/>
+  <int value="14" label="UNKOWN"/>
 </enum>
 
 <enum name="ServiceWorkerReadResponseResult" type="int">