Add UMA for how long service workers run for.

content/browser/service_worker/embedded_worker_registry.h

Index: content/browser/service_worker/embedded_worker_registry.h
diff --git a/content/browser/service_worker/embedded_worker_registry.h b/content/browser/service_worker/embedded_worker_registry.h
index 75b7666cad52371ab84242ee06aa7b6926c86fbb..14bd8b8b44ed3c4bb9de34a3763871ccafc09e43 100644
--- a/content/browser/service_worker/embedded_worker_registry.h
+++ b/content/browser/service_worker/embedded_worker_registry.h
@@ -15,6 +15,7 @@
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
 #include "base/strings/string16.h"
+#include "content/browser/service_worker/service_worker_lifetime_tracker.h"
 #include "content/common/content_export.h"
 #include "content/common/service_worker/service_worker_status_code.h"
 
@@ -83,6 +84,9 @@ class CONTENT_EXPORT EmbeddedWorkerRegistry
                               const base::string16& message,
                               int line_number,
                               const GURL& source_url);
+  // Called by EmbeddedWorkerInstance when it learns DevTools has attached to
+  // it.
+  void OnDevToolsAttached(int embedded_worker_id);
 
   // Removes information about the service workers running on the process and
   // calls ServiceWorkerVersion::OnDetached() on each. Called when the process
@@ -142,6 +146,7 @@ class CONTENT_EXPORT EmbeddedWorkerRegistry
 
   int next_embedded_worker_id_;
   const int initial_embedded_worker_id_;
+  ServiceWorkerLifetimeTracker lifetime_tracker_;
 
   DISALLOW_COPY_AND_ASSIGN(EmbeddedWorkerRegistry);
 };