Add UMA for how long service workers run for.

content/browser/service_worker/service_worker_lifetime_tracker.cc

Index: content/browser/service_worker/service_worker_lifetime_tracker.cc
diff --git a/content/browser/service_worker/service_worker_lifetime_tracker.cc b/content/browser/service_worker/service_worker_lifetime_tracker.cc
new file mode 100644
index 0000000000000000000000000000000000000000..4691bddfce4fd2fb662a45df72e8dcccfd1bd958
--- /dev/null
+++ b/content/browser/service_worker/service_worker_lifetime_tracker.cc
@@ -0,0 +1,45 @@
+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "content/browser/service_worker/service_worker_lifetime_tracker.h"
+
+#include "base/bind.h"
+#include "base/stl_util.h"
+#include "base/time/default_tick_clock.h"
+#include "content/browser/service_worker/service_worker_metrics.h"
+
+namespace content {
+
+ServiceWorkerLifetimeTracker::ServiceWorkerLifetimeTracker()
+    : ServiceWorkerLifetimeTracker(base::MakeUnique<base::DefaultTickClock>()) {
+}
+
+ServiceWorkerLifetimeTracker::ServiceWorkerLifetimeTracker(
+    std::unique_ptr<base::TickClock> tick_clock)
+    : tick_clock_(std::move(tick_clock)) {}
+
+ServiceWorkerLifetimeTracker::~ServiceWorkerLifetimeTracker() = default;
+
+void ServiceWorkerLifetimeTracker::StartTiming(int64_t embedded_worker_id) {
+  DCHECK(!base::ContainsKey(running_workers_, embedded_worker_id));
+
+  running_workers_[embedded_worker_id] = tick_clock_->NowTicks();
+}
+
+void ServiceWorkerLifetimeTracker::StopTiming(int64_t embedded_worker_id) {
+  auto it = running_workers_.find(embedded_worker_id);
+  if (it == running_workers_.end())
+    return;
+  ServiceWorkerMetrics::RecordRuntime(tick_clock_->NowTicks() - it->second);
+  running_workers_.erase(it);
+}
+
+void ServiceWorkerLifetimeTracker::AbortTiming(int64_t embedded_worker_id) {
+  auto it = running_workers_.find(embedded_worker_id);
+  if (it == running_workers_.end())
+    return;
+  running_workers_.erase(it);
+}
+
+}  // namespace content