[Device Service] Move PowerMonitor into the Device Service

content/browser/browser_context.cc

 // Copyright (c) 2012 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/public/browser/browser_context.h"
 
 #include <stddef.h>
 #include <stdint.h>
 #include <algorithm>
 #include <limits>
@@ skipping 440 matching lines @@
         new BrowserContextServiceManagerConnectionHolder(
             service_manager_connection->GetConnector()->Connect(&params),
             std::move(service_request));
     browser_context->SetUserData(kServiceManagerConnection, connection_holder);
 
     ServiceManagerConnection* connection =
         connection_holder->service_manager_connection();
     connection->Start();
 
     // New embedded service factories should be added to |connection| here.
-    // TODO(blundell): Does this belong as a global service rather than per
-    // BrowserContext?
+    // As we've configured service manager to treat device service as singleton,
+    // only one device service instance will be created to serve multiple user
+    // ids.
     ServiceInfo info;
     info.factory =
         base::Bind(&device::CreateDeviceService,

[blundell, 2017/01/03 15:20:50]

Does the Device Service not still need to be registered with
ServiceManagerContext for child processes other than the renderer to be able to
connect to it?

[Ken Rockot(use gerrit already), 2017/01/03 20:25:15]

The answer to your question is yes, but there's another subtle issue this makes
me realize. If a renderer happens to be the first thing to connect to the device
service, then the singleton instance lifetime will be bound to this
BrowserContext via ServiceManagerConnectionImpl. This could lead to service
flakiness if that profile is then destroyed some time later.

I think the right thing to do is completely remove this registration from
BrowserContext, add it to ServiceManagerContext instead; and then also have
ServiceManagerContext initiate and maintain a connection to the device service
on startup. For now, this will ensure that a singleton instance already exists
by the time any real client connects to it.

Once we have a better way to package the device service we can kill the early
connection to it.

[leonhsl(Using Gerrit), 2017/01/04 07:34:11]

Done and thanks a lot for the kindly explanations!

                    BrowserThread::GetTaskRunnerForThread(BrowserThread::FILE));
     connection->AddEmbeddedService(device::mojom::kServiceName, info);
 
     if (base::CommandLine::ForCurrentProcess()->HasSwitch(
             switches::kMojoLocalStorage)) {
       ServiceInfo info;
       info.factory =
           base::Bind(&file::CreateFileService,
                      BrowserThread::GetTaskRunnerForThread(BrowserThread::FILE),
                      BrowserThread::GetTaskRunnerForThread(BrowserThread::DB));
@@ skipping 52 matching lines @@
   if (GetUserData(kDownloadManagerKeyName))
     GetDownloadManager(this)->Shutdown();
 }
 
 void BrowserContext::ShutdownStoragePartitions() {
   if (GetUserData(kStoragePartitionMapKeyName))
     RemoveUserData(kStoragePartitionMapKeyName);
 }
 
 }  // namespace content