ServiceWorker: Keep the worker alive until FetchEvent.waitUntil settles

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 c9298f5c34de2810487677459e9cc51a3b8196aa..c32c3b248d9f37371bb4ccedca96d7036ed906e6 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -50648,8 +50648,7 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <owner>jeremyarcher@chromium.org</owner>
   <summary>
     The time taken between dispatching a FetchEvent to a Service Worker and
-    receiving a fallback-to-network reply. Includes the time for the waitUntil()
-    promise to settle, if any.
+    receiving a fallback-to-network reply.
   </summary>
 </histogram>
 
@@ -50693,6 +50692,16 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="ServiceWorker.FetchEvent.WaitUntil.Time" units="ms">
+  <owner>shimazu@chromium.org</owner>
+  <summary>
+    The time taken between dispatching a FetchEvent to a Service Worker and
+    finishing the FetchEvent. Includes the time for the waitUntil() promise to
+    settle. If there is no waitUntil promise, this will be almost the same with
+    HasResponse.Time or Fallback.Time.
+  </summary>
+</histogram>
+
 <histogram name="ServiceWorker.FetchEventExecutionTime" units="ms">
   <owner>shimazu@chromium.org</owner>
   <obsolete>
@@ -50722,6 +50731,16 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="ServiceWorker.ForeignFetchEvent.WaitUntil.Time" units="ms">
+  <owner>shimazu@chromium.org</owner>
+  <summary>
+    The time taken between dispatching a ForeignFetchEvent to a Service Worker
+    and finishing the ForeignFetch. Includes the time for the waitUntil()
+    promise to settle. If there is no waitUntil promise, this will be almost the
+    same with HasResponse.Time or Fallback.Time.
+  </summary>
+</histogram>
+
 <histogram name="ServiceWorker.InstallEvent.Time" units="ms">
   <owner>shimazu@chromium.org</owner>
   <summary>
@@ -88751,6 +88770,8 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="13" label="FETCH_SUB_RESOURCE"/>
   <int value="14" label="UNKNOWN"/>
   <int value="15" label="FOREIGN_FETCH"/>
+  <int value="16" label="FETCH_WAITUNTIL"/>
+  <int value="17" label="FOREIGN_FETCH_WAITUNTIL"/>
 </enum>
 
 <enum name="ServiceWorkerReadResponseResult" type="int">