First step to refactor ServiceWorkerVersion to make event dispatching more modular.

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 621ef5a00c716dbeeac05a36422b35be515d6832..8c44dfe8e22d675181552a530662674c2a0cee6d 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -43716,7 +43716,7 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 </histogram>
 
 <histogram name="ServiceWorker.RequestTimeouts.Count"
-    enum="ServiceWorkerVersion.RequestType">
+    enum="ServiceWorkerMetrics.EventType">
   <owner>jeremyarcher@google.com</owner>
   <summary>
     The number of Service Worker request timeouts, by request type.
@@ -76345,6 +76345,17 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="2" label="All"/>
 </enum>
 
+<enum name="ServiceWorkerMetrics.EventType" type="int">
+  <int value="0" label="ACTIVATE"/>
+  <int value="1" label="INSTALL"/>
+  <int value="2" label="FETCH"/>
+  <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"/>
+</enum>
+
 <enum name="ServiceWorkerReadResponseResult" type="int">
   <int value="0" label="OK"/>
   <int value="1" label="Read headers error"/>
@@ -76430,17 +76441,6 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="18" label="REQUEST_JOB_ERROR_DESTROYED_WITH_STREAM"/>
 </enum>
 
-<enum name="ServiceWorkerVersion.RequestType" type="int">
-  <int value="0" label="REQUEST_ACTIVATE"/>
-  <int value="1" label="REQUEST_INSTALL"/>
-  <int value="2" label="REQUEST_FETCH"/>
-  <int value="3" label="REQUEST_SYNC"/>
-  <int value="4" label="REQUEST_NOTIFICATION_CLICK"/>
-  <int value="5" label="REQUEST_PUSH"/>
-  <int value="6" label="REQUEST_GEOFENCING"/>
-  <int value="7" label="REQUEST_SERVICE_PORT_CONNECT"/>
-</enum>
-
 <enum name="ServiceWorkerWriteResponseResult" type="int">
   <int value="0" label="OK"/>
   <int value="1" label="Write headers error"/>