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

content/browser/service_worker/service_worker_metrics.h

Index: content/browser/service_worker/service_worker_metrics.h
diff --git a/content/browser/service_worker/service_worker_metrics.h b/content/browser/service_worker/service_worker_metrics.h
index aca36c9e351e3bebeceacdef260a0b22e1c7df25..b8b4db4837f3bf2927ea314a271b463b59c2ba16 100644
--- a/content/browser/service_worker/service_worker_metrics.h
+++ b/content/browser/service_worker/service_worker_metrics.h
@@ -95,6 +95,9 @@ class ServiceWorkerMetrics {
     FETCH_SUB_RESOURCE = 13,
     UNKNOWN = 14,  // Used when event type is not known.
     FOREIGN_FETCH = 15,
+    NAVIGATION_HINT_LINK_MOUSE_DOWN = 16,
+    NAVIGATION_HINT_LINK_TAP_UNCONFIRMED = 17,
+    NAVIGATION_HINT_LINK_TAP_DOWN = 18,
     // Add new events to record here.
     NUM_TYPES
   };
@@ -122,6 +125,9 @@ class ServiceWorkerMetrics {
   // Converts an event type to a string. Used for tracing.
   static const char* EventTypeToString(EventType event_type);
 
+  // Returns true when the event is for a navigation hint.
+  static bool IsNavigationHintEvent(EventType event_type);
+
   // Excludes NTP scope from UMA for now as it tends to dominate the stats and
   // makes the results largely skewed. Some metrics don't follow this policy
   // and hence don't call this function.
@@ -177,6 +183,13 @@ class ServiceWorkerMetrics {
                                       size_t handled_events,
                                       size_t fired_events);
 
+  // Records the precision of the speculative launch of Service Workers for
+  // each navigation hint type when the worker is stopped. If there was no
+  // event fetched to the worker, |event_fired| is false. This means that the
+  // speculative launch was meaningless.
+  static void RecordNavigationHintPrecision(EventType start_worker_purpose,
+                                            bool event_fired);
+
   // Records how often a dispatched event times out.
   static void RecordEventTimeout(EventType event);