Add UMA for how long service workers run for.

content/browser/service_worker/service_worker_context_core.cc

Index: content/browser/service_worker/service_worker_context_core.cc
diff --git a/content/browser/service_worker/service_worker_context_core.cc b/content/browser/service_worker/service_worker_context_core.cc
index a0bbc665b4cbcdbdb437d04c5d49de1439778830..1bf42f4b5258d488947a7da324c161834e8a1a90 100644
--- a/content/browser/service_worker/service_worker_context_core.cc
+++ b/content/browser/service_worker/service_worker_context_core.cc
@@ -750,6 +750,18 @@ int ServiceWorkerContextCore::GetVersionFailureCount(int64_t version_id) {
 
 void ServiceWorkerContextCore::OnRunningStateChanged(
     ServiceWorkerVersion* version) {
+  switch (version->running_status()) {
+    case EmbeddedWorkerStatus::STOPPED:
+      lifetime_tracker_.StopTiming(version->version_id());
+      break;
+    case EmbeddedWorkerStatus::RUNNING:
+      lifetime_tracker_.StartTiming(version->version_id());
+      break;
+    case EmbeddedWorkerStatus::STARTING:
+    case EmbeddedWorkerStatus::STOPPING:
+      break;
+  }

[falken, 2017/02/24 08:32:26]

Hm it looks like I should just add lifetime_tracker_ to observer_list_, then we
shouldn't need this extra code.

+
   if (!observer_list_)
     return;
   observer_list_->Notify(FROM_HERE,
@@ -846,6 +858,11 @@ void ServiceWorkerContextCore::OnControlleeRemoved(
                          version->version_id(), provider_host->client_uuid());
 }
 
+void ServiceWorkerContextCore::OnDevToolsAttached(
+    ServiceWorkerVersion* version) {
+  lifetime_tracker_.AbortTiming(version->version_id());
+}
+
 ServiceWorkerProcessManager* ServiceWorkerContextCore::process_manager() {
   return wrapper_->process_manager();
 }