Remove SetupOnUIThread for EmbeddedWorkerInstance

Thanks to ServiceWorkerOnUI, we can eliminate the class and function to
manage thread-hoppings for starting a service worker. This CL moves
tasks in SetupOnUIThread into EmbeddedWorkerInstance::Start().

Bug: 1138155
Change-Id: I15c72d0d45e792e229a4a8f19972b5d90253fc87
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2578717
Commit-Queue: Makoto Shimazu <shimazu@chromium.org>
Reviewed-by: Asami Doi <asamidoi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#835989}

content/browser/service_worker/embedded_worker_instance.h

@@ -59,7 +59,7 @@ FORWARD_DECLARE_TEST(ServiceWorkerNewScriptLoaderTest, AccessedNetwork);
 // may be 'in-waiting' or running in one of the child processes added by
 // AddProcessReference().
 //
-// Owned by ServiceWorkerVersion. Lives on the core thread.
+// Owned by ServiceWorkerVersion.
 class CONTENT_EXPORT EmbeddedWorkerInstance
     : public blink::mojom::EmbeddedWorkerInstanceHost {
  public:
@@ -264,7 +264,7 @@ class CONTENT_EXPORT EmbeddedWorkerInstance
  private:
   typedef base::ObserverList<Listener>::Unchecked ListenerList;
   class ScopedLifetimeTracker;
-  class StartTask;
+  struct StartInfo;
   class WorkerProcessHandle;
   friend class EmbeddedWorkerInstanceTest;
   FRIEND_TEST_ALL_PREFIXES(EmbeddedWorkerInstanceTest, StartAndStop);
@@ -274,21 +274,14 @@ class CONTENT_EXPORT EmbeddedWorkerInstance
                                ServiceWorkerNewScriptLoaderTest,
                            AccessedNetwork);
 
-  // Called back from StartTask after a process is allocated on the UI thread.
   void OnProcessAllocated(std::unique_ptr<WorkerProcessHandle> handle,
                           ServiceWorkerMetrics::StartSituation start_situation);
-
-  // Called back from StartTask after the worker is registered to
-  // WorkerDevToolsManager.
   void OnRegisteredToDevToolsManager(
-      std::unique_ptr<DevToolsProxy> devtools_proxy,
-      bool wait_for_debugger);
-
+      std::unique_ptr<DevToolsProxy> devtools_proxy);
   // Sends the StartWorker message to the renderer.
   void SendStartWorker(blink::mojom::EmbeddedWorkerStartParamsPtr params);
 
   // Implements blink::mojom::EmbeddedWorkerInstanceHost.
-  // These functions all run on the core thread.
   void RequestTermination(RequestTerminationCallback callback) override;
   void CountFeature(blink::mojom::WebFeature feature) override;
   void OnReadyForInspection(
@@ -325,7 +318,6 @@ class CONTENT_EXPORT EmbeddedWorkerInstance
                      blink::ServiceWorkerStatusCode status);
 
   // Called when a foreground service worker is added/removed in a process.
-  // Called on the core thread and dispatches task to the UI thread.
   void NotifyForegroundServiceWorkerAdded();
   void NotifyForegroundServiceWorkerRemoved();
 
@@ -354,7 +346,6 @@ class CONTENT_EXPORT EmbeddedWorkerInstance
   // using it. The renderer process will disconnect the pipe when appropriate.
   mojo::Remote<blink::mojom::EmbeddedWorkerInstanceClient> client_;
 
-  // Receiver for EmbeddedWorkerInstanceHost, runs on core thread.
   mojo::AssociatedReceiver<EmbeddedWorkerInstanceHost> instance_host_receiver_{
       this};
 
@@ -372,7 +363,9 @@ class CONTENT_EXPORT EmbeddedWorkerInstance
   ListenerList listener_list_;
   std::unique_ptr<DevToolsProxy> devtools_proxy_;
 
-  std::unique_ptr<StartTask> inflight_start_task_;
+  // Contains info to be recorded on completing StartWorker sequence.
+  // Set on Start() and cleared on OnStarted().
+  std::unique_ptr<StartInfo> inflight_start_info_;
   std::unique_ptr<ScopedLifetimeTracker> lifetime_tracker_;
 
   // This is valid only after a process is allocated for the worker.
@@ -386,8 +379,6 @@ class CONTENT_EXPORT EmbeddedWorkerInstance
   mojo::SelfOwnedReceiverRef<network::mojom::URLLoaderFactory>
       script_loader_factory_;
 
-  const scoped_refptr<base::SequencedTaskRunner> ui_task_runner_;
-
   // Remote interface to talk to a running service worker. Used to update
   // subresource loader factories in the service worker.
   mojo::Remote<blink::mojom::SubresourceLoaderUpdater>

content/browser/service_worker/service_worker_metrics.h

@@ -157,9 +157,6 @@ class ServiceWorkerMetrics {
 
     // The browser received the worker started IPC.
     base::TimeTicks local_end;
-
-    // Counts the time overhead of UI/IO thread hops during startup.
-    base::TimeDelta thread_hop_time;
   };
 
   // Converts an event type to a string. Used for tracing.