Revert of Provide the DeviceManager service to the renderer directly, no app.

device/devices_app/devices_app.h

Index: device/devices_app/devices_app.h
diff --git a/device/devices_app/devices_app.h b/device/devices_app/devices_app.h
index 1671570766fd2828c5e1a2e09314475f58a178cc..cac12f4d7fcf9dc11b80e4c0e0b9e7c66372a4fe 100644
--- a/device/devices_app/devices_app.h
+++ b/device/devices_app/devices_app.h
@@ -12,6 +12,10 @@
 #include "mojo/application/public/cpp/application_delegate.h"
 #include "mojo/application/public/cpp/interface_factory.h"
 
+namespace base {
+class SequencedTaskRunner;
+}
+
 namespace mojo {
 class ApplicationImpl;
 }
@@ -25,7 +29,8 @@
 class DevicesApp : public mojo::ApplicationDelegate,
                    public mojo::InterfaceFactory<usb::DeviceManager> {
  public:
-  DevicesApp();
+  explicit DevicesApp(
+      scoped_refptr<base::SequencedTaskRunner> service_task_runner);
   ~DevicesApp() override;
 
  private:
@@ -51,6 +56,7 @@
 
   mojo::ApplicationImpl* app_impl_;
   scoped_ptr<USBServiceInitializer> service_initializer_;
+  scoped_refptr<base::SequencedTaskRunner> service_task_runner_;
   size_t active_device_manager_count_;
 
   // Callback used to shut down the app after a period of inactivity.