Introduce ServiceWorker.ActivatedWorkerPreparationForMainFrame.Time UMA.

content/browser/service_worker/embedded_worker_instance.cc

 // Copyright 2013 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/embedded_worker_instance.h"
 
 #include <utility>
 
 #include "base/bind_helpers.h"
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/threading/non_thread_safe.h"
 #include "base/trace_event/trace_event.h"
 #include "content/browser/devtools/service_worker_devtools_manager.h"
 #include "content/browser/service_worker/embedded_worker_registry.h"
+#include "content/browser/service_worker/embedded_worker_status.h"
 #include "content/browser/service_worker/service_worker_context_core.h"
 #include "content/common/content_switches_internal.h"
 #include "content/common/mojo/service_registry_impl.h"
 #include "content/common/service_worker/embedded_worker_messages.h"
 #include "content/common/service_worker/embedded_worker_settings.h"
 #include "content/common/service_worker/embedded_worker_setup.mojom.h"
 #include "content/common/service_worker/service_worker_types.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/content_browser_client.h"
 #include "content/public/browser/render_process_host.h"
@@ skipping 182 matching lines @@
 // We can abort starting worker by destroying this task anytime during the
 // sequence.
 class EmbeddedWorkerInstance::StartTask {
  public:
   enum class ProcessAllocationState { NOT_ALLOCATED, ALLOCATING, ALLOCATED };
 
   StartTask(EmbeddedWorkerInstance* instance, const GURL& script_url)
       : instance_(instance),
         state_(ProcessAllocationState::NOT_ALLOCATED),
         is_installed_(false),
-        start_situation_(ServiceWorkerMetrics::StartSituation::UNKNOWN),
+        started_during_browser_startup_(false),
         weak_factory_(this) {
     TRACE_EVENT_ASYNC_BEGIN1("ServiceWorker", "EmbeddedWorkerInstance::Start",
                              this, "Script", script_url.spec());
   }
 
   ~StartTask() {
     DCHECK_CURRENTLY_ON(BrowserThread::IO);
     TRACE_EVENT_ASYNC_END0("ServiceWorker", "EmbeddedWorkerInstance::Start",
                            this);
 
@@ skipping 26 matching lines @@
   }
 
   void Start(std::unique_ptr<EmbeddedWorkerMsg_StartWorker_Params> params,
              const StatusCallback& callback) {
     DCHECK_CURRENTLY_ON(BrowserThread::IO);
     state_ = ProcessAllocationState::ALLOCATING;
     start_callback_ = callback;
     is_installed_ = params->is_installed;
 
     if (!GetContentClient()->browser()->IsBrowserStartupComplete())
-      start_situation_ = ServiceWorkerMetrics::StartSituation::DURING_STARTUP;
+      started_during_browser_startup_ = true;
 
     GURL scope(params->scope);
     GURL script_url(params->script_url);
 
     bool can_use_existing_process =
         instance_->context_->GetVersionFailureCount(
             params->service_worker_version_id) < kMaxSameProcessFailureCount;
     instance_->context_->process_manager()->AllocateWorkerProcess(
         instance_->embedded_worker_id_, scope, script_url,
         can_use_existing_process,
         base::Bind(&StartTask::OnProcessAllocated, weak_factory_.GetWeakPtr(),
                    base::Passed(&params)));
   }
 
   static void RunStartCallback(StartTask* task,
                                ServiceWorkerStatusCode status) {
     DCHECK_CURRENTLY_ON(BrowserThread::IO);
     StatusCallback callback = task->start_callback_;
     task->start_callback_.Reset();
     callback.Run(status);
     // |task| may be destroyed.
   }
 
   bool is_installed() const { return is_installed_; }
-  ServiceWorkerMetrics::StartSituation start_situation() const {
-    return start_situation_;
-  }
 
  private:
   void OnProcessAllocated(
       std::unique_ptr<EmbeddedWorkerMsg_StartWorker_Params> params,
       ServiceWorkerStatusCode status,
       int process_id,
       bool is_new_process,
       const EmbeddedWorkerSettings& settings) {
     DCHECK_CURRENTLY_ON(BrowserThread::IO);
 
     if (status != SERVICE_WORKER_OK) {
       TRACE_EVENT_ASYNC_STEP_PAST1(
           "ServiceWorker", "EmbeddedWorkerInstance::Start", this,
           "OnProcessAllocated", "Error", ServiceWorkerStatusToString(status));
       DCHECK_EQ(ChildProcessHost::kInvalidUniqueID, process_id);
       StatusCallback callback = start_callback_;
       start_callback_.Reset();
       instance_->OnStartFailed(callback, status);
       // |this| may be destroyed.
       return;
     }
 
     TRACE_EVENT_ASYNC_STEP_PAST1(
         "ServiceWorker", "EmbeddedWorkerInstance::Start", this,
         "OnProcessAllocated", "Is New Process", is_new_process);
     if (is_installed_)
       ServiceWorkerMetrics::RecordProcessCreated(is_new_process);
 
-    if (start_situation_ == ServiceWorkerMetrics::StartSituation::UNKNOWN) {
-      if (is_new_process)
-        start_situation_ = ServiceWorkerMetrics::StartSituation::NEW_PROCESS;
-      else
-        start_situation_ =
-            ServiceWorkerMetrics::StartSituation::EXISTING_PROCESS;
-    }
+    ServiceWorkerMetrics::StartSituation start_situation =
+        ServiceWorkerMetrics::StartSituation::UNKNOWN;
+    if (started_during_browser_startup_)
+      start_situation = ServiceWorkerMetrics::StartSituation::DURING_STARTUP;
+    else if (is_new_process)
+      start_situation = ServiceWorkerMetrics::StartSituation::NEW_PROCESS;
+    else
+      start_situation = ServiceWorkerMetrics::StartSituation::EXISTING_PROCESS;
 
     // Notify the instance that a process is allocated.
     state_ = ProcessAllocationState::ALLOCATED;
-    instance_->OnProcessAllocated(base::WrapUnique(new WorkerProcessHandle(
-        instance_->context_, instance_->embedded_worker_id(), process_id,
-        is_new_process)));
+    instance_->OnProcessAllocated(
+        base::WrapUnique(new WorkerProcessHandle(
+            instance_->context_, instance_->embedded_worker_id(), process_id,
+            is_new_process)),
+        start_situation);
 
     // TODO(bengr): Support changes to this setting while the worker
     // is running.
     params->settings.data_saver_enabled = settings.data_saver_enabled;
 
     // Register the instance to DevToolsManager on UI thread.
     const int64_t service_worker_version_id = params->service_worker_version_id;
     const GURL& scope = params->scope;
     GURL script_url(params->script_url);
     BrowserThread::PostTask(
@@ skipping 47 matching lines @@
   }
 
   // |instance_| must outlive |this|.
   EmbeddedWorkerInstance* instance_;
 
   StatusCallback start_callback_;
   ProcessAllocationState state_;
 
   // Used for UMA.
   bool is_installed_;
-  ServiceWorkerMetrics::StartSituation start_situation_;
+  bool started_during_browser_startup_;
 
   base::WeakPtrFactory<StartTask> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(StartTask);
 };
 
 bool EmbeddedWorkerInstance::Listener::OnMessageReceived(
     const IPC::Message& message) {
   return false;
 }
 
 EmbeddedWorkerInstance::~EmbeddedWorkerInstance() {
-  DCHECK(status_ == STOPPING || status_ == STOPPED) << status_;
+  DCHECK(status_ == EmbeddedWorkerStatus::STOPPING ||
+         status_ == EmbeddedWorkerStatus::STOPPED)
+      << static_cast<int>(status_);
   devtools_proxy_.reset();
   if (registry_->GetWorker(embedded_worker_id_))
     registry_->RemoveWorker(process_id(), embedded_worker_id_);
   process_handle_.reset();
 }
 
 void EmbeddedWorkerInstance::Start(
     std::unique_ptr<EmbeddedWorkerMsg_StartWorker_Params> params,
     const StatusCallback& callback) {
   if (!context_) {
     callback.Run(SERVICE_WORKER_ERROR_ABORT);
     // |this| may be destroyed by the callback.
     return;
   }
-  DCHECK(status_ == STOPPED);
+  DCHECK(status_ == EmbeddedWorkerStatus::STOPPED);
 
   DCHECK(!params->pause_after_download || !params->is_installed);
   DCHECK_NE(kInvalidServiceWorkerVersionId, params->service_worker_version_id);
   step_time_ = base::TimeTicks::Now();
-  status_ = STARTING;
+  status_ = EmbeddedWorkerStatus::STARTING;
   starting_phase_ = ALLOCATING_PROCESS;
   network_accessed_for_script_ = false;
   service_registry_.reset(new ServiceRegistryImpl());
   FOR_EACH_OBSERVER(Listener, listener_list_, OnStarting());
 
   params->embedded_worker_id = embedded_worker_id_;
   params->worker_devtools_agent_route_id = MSG_ROUTING_NONE;
   params->wait_for_debugger = false;
   params->settings.v8_cache_options = GetV8CacheOptions();
 
   inflight_start_task_.reset(new StartTask(this, params->script_url));
   inflight_start_task_->Start(std::move(params), callback);
 }
 
 ServiceWorkerStatusCode EmbeddedWorkerInstance::Stop() {
-  DCHECK(status_ == STARTING || status_ == RUNNING) << status_;
+  DCHECK(status_ == EmbeddedWorkerStatus::STARTING ||
+         status_ == EmbeddedWorkerStatus::RUNNING)
+      << static_cast<int>(status_);
 
   // Abort an inflight start task.
   inflight_start_task_.reset();
 
   ServiceWorkerStatusCode status =
       registry_->StopWorker(process_id(), embedded_worker_id_);
   UMA_HISTOGRAM_ENUMERATION("ServiceWorker.SendStopWorker.Status", status,
                             SERVICE_WORKER_ERROR_MAX_VALUE);
   // StopWorker could fail if we were starting up and don't have a process yet,
   // or we can no longer communicate with the process. So just detach.
   if (status != SERVICE_WORKER_OK) {
     OnDetached();
     return status;
   }
 
-  status_ = STOPPING;
+  status_ = EmbeddedWorkerStatus::STOPPING;
   FOR_EACH_OBSERVER(Listener, listener_list_, OnStopping());
   return status;
 }
 
 void EmbeddedWorkerInstance::StopIfIdle() {
   if (devtools_attached_) {
     if (devtools_proxy_)
       devtools_proxy_->NotifyWorkerStopIgnored();
     return;
   }
   Stop();
 }
 
 ServiceWorkerStatusCode EmbeddedWorkerInstance::SendMessage(
     const IPC::Message& message) {
   DCHECK_NE(kInvalidEmbeddedWorkerThreadId, thread_id_);
-  if (status_ != RUNNING && status_ != STARTING)
+  if (status_ != EmbeddedWorkerStatus::RUNNING &&
+      status_ != EmbeddedWorkerStatus::STARTING) {
     return SERVICE_WORKER_ERROR_IPC_FAILED;
+  }
   return registry_->Send(process_id(),
                          new EmbeddedWorkerContextMsg_MessageToWorker(
                              thread_id_, embedded_worker_id_, message));
 }
 
 void EmbeddedWorkerInstance::ResumeAfterDownload() {
-  if (process_id() == ChildProcessHost::kInvalidUniqueID || status_ != STARTING)
+  if (process_id() == ChildProcessHost::kInvalidUniqueID ||
+      status_ != EmbeddedWorkerStatus::STARTING) {
     return;
+  }
   registry_->Send(process_id(), new EmbeddedWorkerMsg_ResumeAfterDownload(
                                     embedded_worker_id_));
 }
 
 ServiceRegistry* EmbeddedWorkerInstance::GetServiceRegistry() {
-  DCHECK(status_ == STARTING || status_ == RUNNING) << status_;
+  DCHECK(status_ == EmbeddedWorkerStatus::STARTING ||
+         status_ == EmbeddedWorkerStatus::RUNNING)
+      << static_cast<int>(status_);
   return service_registry_.get();
 }
 
 EmbeddedWorkerInstance::EmbeddedWorkerInstance(
     base::WeakPtr<ServiceWorkerContextCore> context,
     int embedded_worker_id)
     : context_(context),
       registry_(context->embedded_worker_registry()),
       embedded_worker_id_(embedded_worker_id),
-      status_(STOPPED),
+      status_(EmbeddedWorkerStatus::STOPPED),
       starting_phase_(NOT_STARTING),
       thread_id_(kInvalidEmbeddedWorkerThreadId),
       devtools_attached_(false),
       network_accessed_for_script_(false),
       weak_factory_(this) {}
 
 void EmbeddedWorkerInstance::OnProcessAllocated(
-    std::unique_ptr<WorkerProcessHandle> handle) {
-  DCHECK_EQ(STARTING, status_);
+    std::unique_ptr<WorkerProcessHandle> handle,
+    ServiceWorkerMetrics::StartSituation start_situation) {
+  DCHECK_EQ(EmbeddedWorkerStatus::STARTING, status_);
   DCHECK(!process_handle_);
 
   process_handle_ = std::move(handle);
   starting_phase_ = REGISTERING_TO_DEVTOOLS;
+  start_situation_ = start_situation;
   FOR_EACH_OBSERVER(Listener, listener_list_, OnProcessAllocated());
 }
 
 void EmbeddedWorkerInstance::OnRegisteredToDevToolsManager(
     bool is_new_process,
     int worker_devtools_agent_route_id,
     bool wait_for_debugger) {
   if (worker_devtools_agent_route_id != MSG_ROUTING_NONE) {
     DCHECK(!devtools_proxy_);
     devtools_proxy_.reset(
         new DevToolsProxy(process_id(), worker_devtools_agent_route_id));
   }
   if (wait_for_debugger) {
     // We don't measure the start time when wait_for_debugger flag is set. So
     // we set the NULL time here.
     step_time_ = base::TimeTicks();
   }
 }
 
 void EmbeddedWorkerInstance::OnStartWorkerMessageSent() {
   if (!step_time_.is_null()) {
     base::TimeDelta duration = UpdateStepTime();
     if (inflight_start_task_->is_installed()) {
-      ServiceWorkerMetrics::RecordTimeToSendStartWorker(
-          duration, inflight_start_task_->start_situation());
+      ServiceWorkerMetrics::RecordTimeToSendStartWorker(duration,
+                                                        start_situation_);
     }
   }
 
   starting_phase_ = SENT_START_WORKER;
   FOR_EACH_OBSERVER(Listener, listener_list_, OnStartWorkerMessageSent());
 }
 
 void EmbeddedWorkerInstance::OnReadyForInspection() {
   if (devtools_proxy_)
     devtools_proxy_->NotifyWorkerReadyForInspection();
@@ skipping 21 matching lines @@
   } else {
     source = LoadSource::HTTP_CACHE;
   }
   TRACE_EVENT_ASYNC_STEP_PAST1(
       "ServiceWorker", "EmbeddedWorkerInstance::Start",
       inflight_start_task_.get(), "OnScriptLoaded", "Source",
       ServiceWorkerMetrics::LoadSourceToString(source));
 
   if (!step_time_.is_null()) {
     base::TimeDelta duration = UpdateStepTime();
-    ServiceWorkerMetrics::RecordTimeToLoad(
-        duration, source, inflight_start_task_->start_situation());
+    ServiceWorkerMetrics::RecordTimeToLoad(duration, source, start_situation_);
   }
 
   starting_phase_ = SCRIPT_LOADED;
   FOR_EACH_OBSERVER(Listener, listener_list_, OnScriptLoaded());
   // |this| may be destroyed by the callback.
 }
 
 void EmbeddedWorkerInstance::OnURLJobCreatedForMainScript() {
   if (!inflight_start_task_)
     return;
   TRACE_EVENT_ASYNC_STEP_PAST0("ServiceWorker", "EmbeddedWorkerInstance::Start",
                                inflight_start_task_.get(), "OnURLJobCreated");
   if (!step_time_.is_null()) {
     base::TimeDelta duration = UpdateStepTime();
     if (inflight_start_task_->is_installed())
-      ServiceWorkerMetrics::RecordTimeToURLJob(
-          duration, inflight_start_task_->start_situation());
+      ServiceWorkerMetrics::RecordTimeToURLJob(duration, start_situation_);
   }
 }
 
 void EmbeddedWorkerInstance::OnWorkerVersionInstalled() {
   if (devtools_proxy_)
     devtools_proxy_->NotifyWorkerVersionInstalled();
 }
 
 void EmbeddedWorkerInstance::OnWorkerVersionDoomed() {
   if (devtools_proxy_)
     devtools_proxy_->NotifyWorkerVersionDoomed();
 }
 
 void EmbeddedWorkerInstance::OnThreadStarted(int thread_id) {
   if (!inflight_start_task_)
     return;
   TRACE_EVENT_ASYNC_STEP_PAST0("ServiceWorker", "EmbeddedWorkerInstance::Start",
                                inflight_start_task_.get(), "OnThreadStarted");
 
   starting_phase_ = THREAD_STARTED;
   if (!step_time_.is_null()) {
     base::TimeDelta duration = UpdateStepTime();
     if (inflight_start_task_->is_installed())
-      ServiceWorkerMetrics::RecordTimeToStartThread(
-          duration, inflight_start_task_->start_situation());
+      ServiceWorkerMetrics::RecordTimeToStartThread(duration, start_situation_);
   }
 
   thread_id_ = thread_id;
   FOR_EACH_OBSERVER(Listener, listener_list_, OnThreadStarted());
 
   shell::mojom::InterfaceProviderPtr exposed_services;
   service_registry_->Bind(GetProxy(&exposed_services));
   shell::mojom::InterfaceProviderPtr services;
   shell::mojom::InterfaceProviderRequest services_request = GetProxy(&services);
   BrowserThread::PostTask(
       BrowserThread::UI, FROM_HERE,
       base::Bind(SetupMojoOnUIThread, process_id(), thread_id_,
                  base::Passed(&services_request),
                  base::Passed(exposed_services.PassInterface())));
   service_registry_->BindRemoteServiceProvider(std::move(services));
 }
 
 void EmbeddedWorkerInstance::OnScriptLoadFailed() {
   if (!inflight_start_task_)
     return;
   TRACE_EVENT_ASYNC_STEP_PAST0("ServiceWorker", "EmbeddedWorkerInstance::Start",
                                inflight_start_task_.get(),
                                "OnScriptLoadFailed");
   FOR_EACH_OBSERVER(Listener, listener_list_, OnScriptLoadFailed());
 }
 
 void EmbeddedWorkerInstance::OnScriptEvaluated(bool success) {
   if (!inflight_start_task_)
     return;
-  DCHECK_EQ(STARTING, status_);
+  DCHECK_EQ(EmbeddedWorkerStatus::STARTING, status_);
 
   TRACE_EVENT_ASYNC_STEP_PAST1("ServiceWorker", "EmbeddedWorkerInstance::Start",
                                inflight_start_task_.get(), "OnScriptEvaluated",
                                "Success", success);
   starting_phase_ = SCRIPT_EVALUATED;
   if (!step_time_.is_null()) {
     base::TimeDelta duration = UpdateStepTime();
     if (success && inflight_start_task_->is_installed())
-      ServiceWorkerMetrics::RecordTimeToEvaluateScript(
-          duration, inflight_start_task_->start_situation());
+      ServiceWorkerMetrics::RecordTimeToEvaluateScript(duration,
+                                                       start_situation_);
   }
 
   base::WeakPtr<EmbeddedWorkerInstance> weak_this = weak_factory_.GetWeakPtr();
   StartTask::RunStartCallback(
       inflight_start_task_.get(),
       success ? SERVICE_WORKER_OK
               : SERVICE_WORKER_ERROR_SCRIPT_EVALUATE_FAILED);
   // |this| may be destroyed by the callback.
 }
 
 void EmbeddedWorkerInstance::OnStarted() {
   // Stop is requested before OnStarted is sent back from the worker.
-  if (status_ == STOPPING)
+  if (status_ == EmbeddedWorkerStatus::STOPPING)
     return;
-  DCHECK(status_ == STARTING);
-  status_ = RUNNING;
+  DCHECK(status_ == EmbeddedWorkerStatus::STARTING);
+  status_ = EmbeddedWorkerStatus::RUNNING;
   inflight_start_task_.reset();
   FOR_EACH_OBSERVER(Listener, listener_list_, OnStarted());
 }
 
 void EmbeddedWorkerInstance::OnStopped() {
-  Status old_status = status_;
+  EmbeddedWorkerStatus old_status = status_;
   ReleaseProcess();
   FOR_EACH_OBSERVER(Listener, listener_list_, OnStopped(old_status));
 }
 
 void EmbeddedWorkerInstance::OnDetached() {
-  Status old_status = status_;
+  EmbeddedWorkerStatus old_status = status_;
   ReleaseProcess();
   FOR_EACH_OBSERVER(Listener, listener_list_, OnDetached(old_status));
 }
 
 void EmbeddedWorkerInstance::Detach() {
   registry_->RemoveWorker(process_id(), embedded_worker_id_);
   OnDetached();
 }
 
 base::WeakPtr<EmbeddedWorkerInstance> EmbeddedWorkerInstance::AsWeakPtr() {
@@ skipping 67 matching lines @@
   starting_phase_ = SCRIPT_DOWNLOADING;
   network_accessed_for_script_ = true;
 }
 
 void EmbeddedWorkerInstance::ReleaseProcess() {
   // Abort an inflight start task.
   inflight_start_task_.reset();
 
   devtools_proxy_.reset();
   process_handle_.reset();
-  status_ = STOPPED;
+  status_ = EmbeddedWorkerStatus::STOPPED;
   thread_id_ = kInvalidEmbeddedWorkerThreadId;
   service_registry_.reset();
 }
 
 void EmbeddedWorkerInstance::OnStartFailed(const StatusCallback& callback,
                                            ServiceWorkerStatusCode status) {
-  Status old_status = status_;
+  EmbeddedWorkerStatus old_status = status_;
   ReleaseProcess();
   base::WeakPtr<EmbeddedWorkerInstance> weak_this = weak_factory_.GetWeakPtr();
   callback.Run(status);
-  if (weak_this && old_status != STOPPED)
+  if (weak_this && old_status != EmbeddedWorkerStatus::STOPPED)
     FOR_EACH_OBSERVER(Listener, weak_this->listener_list_,
                       OnStopped(old_status));
 }
 
 base::TimeDelta EmbeddedWorkerInstance::UpdateStepTime() {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
   DCHECK(!step_time_.is_null());
   base::TimeTicks now = base::TimeTicks::Now();
   base::TimeDelta duration = now - step_time_;
   step_time_ = now;
   return duration;
 }
 
 void EmbeddedWorkerInstance::AddMessageToConsole(ConsoleMessageLevel level,
                                                  const std::string& message) {
-  if (status_ != RUNNING && status_ != STARTING)
+  if (status_ != EmbeddedWorkerStatus::RUNNING &&
+      status_ != EmbeddedWorkerStatus::STARTING) {
     return;
+  }
   registry_->Send(process_id(), new EmbeddedWorkerMsg_AddMessageToConsole(
                                     embedded_worker_id_, level, message));
 }
 
 // static
-std::string EmbeddedWorkerInstance::StatusToString(Status status) {
+std::string EmbeddedWorkerInstance::StatusToString(
+    EmbeddedWorkerStatus status) {
   switch (status) {
-    case STOPPED:
+    case EmbeddedWorkerStatus::STOPPED:
       return "STOPPED";
-    case STARTING:
+    case EmbeddedWorkerStatus::STARTING:
       return "STARTING";
-    case RUNNING:
+    case EmbeddedWorkerStatus::RUNNING:
       return "RUNNING";
-    case STOPPING:
+    case EmbeddedWorkerStatus::STOPPING:
       return "STOPPING";
   }
-  NOTREACHED() << status;
+  NOTREACHED();

[falken, 2016/06/07 06:20:30]

curious: why remove the status output?

[horo, 2016/06/07 06:58:48]

Done.

   return std::string();
 }
 
 // static
 std::string EmbeddedWorkerInstance::StartingPhaseToString(StartingPhase phase) {
   switch (phase) {
     case NOT_STARTING:
       return "Not in STARTING status";
     case ALLOCATING_PROCESS:
       return "Allocating process";
@@ skipping 14 matching lines @@
     case SCRIPT_READ_FINISHED:
       return "Script read finished";
     case STARTING_PHASE_MAX_VALUE:
       NOTREACHED();
   }
   NOTREACHED() << phase;
   return std::string();
 }
 
 }  // namespace content