Introduce ServiceWorker.ActivatedWorkerPreparationForMainFrame.Time UMA.

content/browser/service_worker/embedded_worker_instance.h

Index: content/browser/service_worker/embedded_worker_instance.h
diff --git a/content/browser/service_worker/embedded_worker_instance.h b/content/browser/service_worker/embedded_worker_instance.h
index 9356bb531f0510aca376961a69e14e50e48f1f6a..a74d3766cec8a9cdb18cfdf4016c5da326815c1d 100644
--- a/content/browser/service_worker/embedded_worker_instance.h
+++ b/content/browser/service_worker/embedded_worker_instance.h
@@ -20,6 +20,7 @@
 #include "base/observer_list.h"
 #include "base/strings/string16.h"
 #include "base/time/time.h"
+#include "content/browser/service_worker/embedded_worker_status.h"
 #include "content/browser/service_worker/service_worker_metrics.h"
 #include "content/common/content_export.h"
 #include "content/common/service_worker/service_worker_status_code.h"
@@ -51,12 +52,7 @@ class ServiceWorkerContextCore;
 class CONTENT_EXPORT EmbeddedWorkerInstance {
  public:
   typedef base::Callback<void(ServiceWorkerStatusCode)> StatusCallback;
-  enum Status {
-    STOPPED,
-    STARTING,
-    RUNNING,
-    STOPPING,
-  };
+  typedef EmbeddedWorkerStatus Status;

[falken, 2016/06/07 03:46:12]

I think it's now:
using EmbeddedWorkerStatus = Status

But I tend to prefer to just write out EmbeddedWorkerStatus to eliminate the
level of indirection.

[horo, 2016/06/07 05:58:12]

Done.

 
   // This enum is used in UMA histograms. Append-only.
   enum StartingPhase {
@@ -142,7 +138,7 @@ class CONTENT_EXPORT EmbeddedWorkerInstance {
   int embedded_worker_id() const { return embedded_worker_id_; }
   Status status() const { return status_; }
   StartingPhase starting_phase() const {
-    DCHECK_EQ(STARTING, status());
+    DCHECK_EQ(Status::STARTING, status());
     return starting_phase_;
   }
   int process_id() const;
@@ -163,6 +159,10 @@ class CONTENT_EXPORT EmbeddedWorkerInstance {
     return network_accessed_for_script_;
   }
 
+  ServiceWorkerMetrics::StartSituation start_situation() const {

[falken, 2016/06/07 03:46:12]

Does it make sense to have DCHECK(STARTING || RUNNING) here?

[horo, 2016/06/07 05:58:12]

Done.

+    return start_situation_;
+  }
+
   // Called when the main script load accessed the network.
   void OnNetworkAccessedForScriptLoad();
 
@@ -208,7 +208,8 @@ class CONTENT_EXPORT EmbeddedWorkerInstance {
                          int embedded_worker_id);
 
   // Called back from StartTask after a process is allocated on the UI thread.
-  void OnProcessAllocated(std::unique_ptr<WorkerProcessHandle> handle);
+  void OnProcessAllocated(std::unique_ptr<WorkerProcessHandle> handle,
+                          ServiceWorkerMetrics::StartSituation start_situation);
 
   // Called back from StartTask after the worker is registered to
   // WorkerDevToolsManager.
@@ -309,6 +310,9 @@ class CONTENT_EXPORT EmbeddedWorkerInstance {
 
   std::unique_ptr<StartTask> inflight_start_task_;
 
+  ServiceWorkerMetrics::StartSituation start_situation_ =
+      ServiceWorkerMetrics::StartSituation::UNKNOWN;

[falken, 2016/06/07 03:46:12]

It's a little unfortunate this state has to move out of StartTask. Can you add
comments about when this member is valid?

[horo, 2016/06/07 05:58:12]

Done.

+
   // Used for UMA. The start time of the current start sequence step.
   base::TimeTicks step_time_;