Replace device_sensor browsertest by service unittest.

services/device/device_service_test_base.h

Index: services/device/device_service_test_base.h
diff --git a/services/device/device_service_test_base.h b/services/device/device_service_test_base.h
index 4df7d1ea4549a6bc14d7cf9410be9c273306e84f..1a87d76d093af0b13741a2474bc12a91926e5b09 100644
--- a/services/device/device_service_test_base.h
+++ b/services/device/device_service_test_base.h
@@ -6,6 +6,7 @@
 #define SERVICES_DEVICE_DEVICE_SERVICE_TEST_BASE_H_
 
 #include "base/macros.h"
+#include "base/threading/thread.h"
 #include "services/service_manager/public/cpp/service_test.h"
 
 namespace device {
@@ -20,6 +21,8 @@ class DeviceServiceTestBase : public service_manager::test::ServiceTest {
   // service_manager::test::ServiceTest:
   std::unique_ptr<service_manager::Service> CreateService() override;
 
+  base::Thread io_thread_;
+
   DISALLOW_COPY_AND_ASSIGN(DeviceServiceTestBase);
 };