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

device/devices_app/devices_app.cc

Index: device/devices_app/devices_app.cc
diff --git a/device/devices_app/devices_app.cc b/device/devices_app/devices_app.cc
index 599c64fce1a4630cb940eaefc38b9ca9dddfde31..134948d9c9229b956ade92efb9f0ea6f29f17476 100644
--- a/device/devices_app/devices_app.cc
+++ b/device/devices_app/devices_app.cc
@@ -72,22 +72,15 @@ class DevicesApp::USBServiceInitializer {
   DISALLOW_COPY_AND_ASSIGN(USBServiceInitializer);
 };
 
-DevicesApp::DevicesApp(
-    scoped_refptr<base::SequencedTaskRunner> service_task_runner)
-    : app_impl_(nullptr),
-      service_task_runner_(service_task_runner),
-      active_device_manager_count_(0) {
-}
+DevicesApp::DevicesApp()
+    : app_impl_(nullptr), active_device_manager_count_(0) {}
 
 DevicesApp::~DevicesApp() {
 }
 
 void DevicesApp::Initialize(mojo::ApplicationImpl* app) {
   app_impl_ = app;
-  if (!service_task_runner_) {
-    service_initializer_.reset(new USBServiceInitializer);
-    service_task_runner_ = base::ThreadTaskRunnerHandle::Get();
-  }
+  service_initializer_.reset(new USBServiceInitializer);
   StartIdleTimer();
 }
 
@@ -110,8 +103,8 @@ void DevicesApp::Create(mojo::ApplicationConnection* connection,
   connection->ConnectToService(&permission_provider);
 
   // Owned by its message pipe.
-  usb::DeviceManagerImpl* device_manager = new usb::DeviceManagerImpl(
-      request.Pass(), permission_provider.Pass(), service_task_runner_);
+  usb::DeviceManagerImpl* device_manager =
+      new usb::DeviceManagerImpl(permission_provider.Pass(), request.Pass());
   device_manager->set_connection_error_handler(
       base::Bind(&DevicesApp::OnConnectionError, base::Unretained(this)));