Observe UsbService from the FILE thread in DevicePermissionsManager.

extensions/browser/api/device_permissions_manager.h

 // Copyright 2014 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.
 
 #ifndef EXTENSIONS_DEVICE_PERMISSION_MANAGER_H_
 #define EXTENSIONS_DEVICE_PERMISSION_MANAGER_H_
 
 #include <map>
 #include <set>
 #include <vector>
 
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/scoped_observer.h"
 #include "base/strings/string16.h"
 #include "base/threading/thread_checker.h"
 #include "components/keyed_service/content/browser_context_keyed_service_factory.h"
 #include "components/keyed_service/core/keyed_service.h"
+#include "content/public/browser/browser_thread.h"
 #include "device/usb/usb_service.h"
 #include "extensions/browser/process_manager.h"
 #include "extensions/browser/process_manager_observer.h"
 
 template <typename T>
 struct DefaultSingletonTraits;
 
 namespace base {
 class Value;
 }
@@ skipping 96 matching lines @@
   std::set<scoped_refptr<DevicePermissionEntry>> entries_;
   std::map<scoped_refptr<device::UsbDevice>,
            scoped_refptr<DevicePermissionEntry>> ephemeral_devices_;
 
   DISALLOW_COPY_AND_ASSIGN(DevicePermissions);
 };
 
 // Manages saved device permissions for all extensions.
 class DevicePermissionsManager : public KeyedService,
                                  public base::NonThreadSafe,
-                                 public ProcessManagerObserver,
-                                 public device::UsbService::Observer {
+                                 public ProcessManagerObserver {
  public:
   static DevicePermissionsManager* Get(content::BrowserContext* context);
 
   // Returns a copy of the DevicePermissions object for a given extension that
   // can be used by any thread.
   scoped_ptr<DevicePermissions> GetForExtension(
       const std::string& extension_id);
 
   // Equivalent to calling GetForExtension and extracting the permission string
   // for each entry.
@@ skipping 15 matching lines @@
                       scoped_refptr<DevicePermissionEntry> entry);
 
   // Revokes permission for the extension to access the given device.
   void RemoveEntry(const std::string& extension_id,
                    scoped_refptr<DevicePermissionEntry> entry);
 
   // Revokes permission for the extension to access all allowed devices.
   void Clear(const std::string& extension_id);
 
  private:
+  class FileThreadHelper;
+
   friend class DevicePermissionsManagerFactory;
   FRIEND_TEST_ALL_PREFIXES(DevicePermissionsManagerTest, SuspendExtension);
 
   DevicePermissionsManager(content::BrowserContext* context);
   ~DevicePermissionsManager() override;
 
   DevicePermissions* Get(const std::string& extension_id) const;
   DevicePermissions* GetOrInsert(const std::string& extension_id);
+  void OnDeviceRemoved(scoped_refptr<device::UsbDevice> device);
 
   // ProcessManagerObserver implementation
   void OnBackgroundHostClose(const std::string& extension_id) override;
 
-  // device::UsbService::Observer implementation
-  void OnDeviceRemoved(scoped_refptr<device::UsbDevice> device) override;
-
   content::BrowserContext* context_;
   std::map<std::string, DevicePermissions*> extension_id_to_device_permissions_;
   ScopedObserver<ProcessManager, ProcessManagerObserver>
       process_manager_observer_;
-  ScopedObserver<device::UsbService, device::UsbService::Observer>
-      usb_service_observer_;
+  FileThreadHelper* helper_;
+
+  base::WeakPtrFactory<DevicePermissionsManager> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(DevicePermissionsManager);
 };
 
 class DevicePermissionsManagerFactory
     : public BrowserContextKeyedServiceFactory {
  public:
   static DevicePermissionsManager* GetForBrowserContext(
       content::BrowserContext* context);
   static DevicePermissionsManagerFactory* GetInstance();
 
  private:
   friend struct DefaultSingletonTraits<DevicePermissionsManagerFactory>;
 
   DevicePermissionsManagerFactory();
   ~DevicePermissionsManagerFactory() override;
 
   // BrowserContextKeyedServiceFactory implementation
   KeyedService* BuildServiceInstanceFor(
       content::BrowserContext* context) const override;
   content::BrowserContext* GetBrowserContextToUse(
       content::BrowserContext* context) const override;
 
   DISALLOW_COPY_AND_ASSIGN(DevicePermissionsManagerFactory);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_DEVICE_PERMISSION_MANAGER_H_