[sensors] Add Generic Sensor platform unit tests.

device/generic_sensor/BUILD.gn

 # Copyright 2016 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.
 
 source_set("generic_sensor") {
   sources = [
     "platform_sensor.cc",
     "platform_sensor.h",
     "platform_sensor_configuration.cc",
     "platform_sensor_configuration.h",
     "platform_sensor_provider.h",
     "platform_sensor_provider_base.cc",
     "platform_sensor_provider_base.h",
     "platform_sensor_provider_default.cc",
     "sensor_impl.cc",
     "sensor_impl.h",
     "sensor_provider_impl.cc",
     "sensor_provider_impl.h",
   ]
 
   deps = [
     "//base",
     "//device/generic_sensor/public/interfaces",
   ]
 }
+
+static_library("mocks") {
+  testonly = true
+  sources = [
+    "mock_platform_sensor.cc",
+    "mock_platform_sensor.h",
+    "mock_platform_sensor_provider.cc",
+    "mock_platform_sensor_provider.h",
+  ]
+
+  deps = [
+    ":generic_sensor",
+    "//base",
+  ]
+}