[WIP] Speculatively launch Service Workers on mouse/touch events.

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 eeea9193acb9d4e9a4283bcdc7b6759c2d6d35be..62b76828b2f4d67715297e690ea729b30a357d9b 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -49806,6 +49806,16 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <summary>Execution time of ServiceWorkerGlobalScope.onmessage.</summary>
 </histogram>
 
+<histogram name="ServiceWorker.NavigationHintPrecision" enum="BooleanEnabled">
+  <owner>horo@google.com</owner>
+  <summary>
+    The precision of the speculative launch of Service Workers for navigation
+    hints. Recorded when the worker is stopped. If there was no event fetched to
+    the worker, this value is false. This means that the speculative launch was
+    meaningless.
+  </summary>
+</histogram>
+
 <histogram name="ServiceWorker.NotificationClickEvent.Time" units="ms">
   <owner>peter@chromium.org</owner>
   <summary>
@@ -79015,6 +79025,7 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="-667517406" label="overscroll-history-navigation"/>
   <int value="-661978438" label="enable-data-reduction-proxy-lo-fi"/>
   <int value="-660160292" label="enable-apps-show-on-first-paint"/>
+  <int value="-650504533" label="enable-speculative-launch-service-worker"/>
   <int value="-649956990" label="enable-harfbuzz-rendertext"/>
   <int value="-641719457" label="disable-compositor-touch-hit-testing"/>
   <int value="-631740127" label="inert-visual-viewport"/>
@@ -96943,6 +96954,12 @@ To add a new entry, add it with any value and run test to compute valid value.
   <suffix name="FETCH_SUB_RESOURCE" label="FETCH_SUB_RESOURCE"/>
   <suffix name="UNKNOWN" label="UNKNOWN"/>
   <suffix name="FOREIGN_FETCH" label="FOREIGN_FETCH"/>
+  <suffix name="NAVIGATION_HINT_LINK_MOUSE_DOWN"
+      label="NAVIGATION_HINT_LINK_MOUSE_DOWN"/>
+  <suffix name="NAVIGATION_HINT_LINK_TAP_UNCONFIRMED"
+      label="NAVIGATION_HINT_LINK_TAP_UNCONFIRMED"/>
+  <suffix name="NAVIGATION_HINT_LINK_TAP_DOWN"
+      label="NAVIGATION_HINT_LINK_TAP_DOWN"/>
   <affected-histogram name="ServiceWorker.StartWorker.StatusByPurpose"/>
   <affected-histogram name="ServiceWorker.StartWorker.Time_DuringStartup"/>
   <affected-histogram name="ServiceWorker.StartWorker.Time_ExistingProcess"/>
@@ -96956,6 +96973,13 @@ To add a new entry, add it with any value and run test to compute valid value.
   <suffix name="3" label="Failed three times."/>
 </histogram_suffixes>
 
+<histogram_suffixes name="ServiceWorker.NavigationHint" separator=".">
+  <suffix name="LINK_MOUSE_DOWN" label="LINK_MOUSE_DOWN"/>
+  <suffix name="LINK_TAP_UNCONFIRMED" label="LINK_TAP_UNCONFIRMED"/>
+  <suffix name="LINK_TAP_DOWN" label="LINK_TAP_DOWN"/>
+  <affected-histogram name="ServiceWorker.NavigationHintPrecision"/>
+</histogram_suffixes>
+
 <histogram_suffixes name="ServiceWorker.ShutdownStatus">
   <affected-histogram name="ServiceWorker.ActivateEventStatus"/>
   <suffix name="InShutdown" label="Browser shutdown started."/>