[sensors] Add Generic Sensor platform unit tests.

device/generic_sensor/fake_platform_sensor_provider.cc

+// 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.
+
+#include "base/memory/singleton.h"
+
+#include "device/generic_sensor/fake_platform_sensor.h"
+#include "device/generic_sensor/fake_platform_sensor_provider.h"
+
+namespace device {
+
+// static
+FakePlatformSensorProvider* FakePlatformSensorProvider::GetInstance() {
+  return base::Singleton<
+      FakePlatformSensorProvider,
+      base::LeakySingletonTraits<FakePlatformSensorProvider>>::get();
+}
+
+FakePlatformSensorProvider::FakePlatformSensorProvider() = default;
+
+FakePlatformSensorProvider::~FakePlatformSensorProvider() = default;
+
+scoped_refptr<PlatformSensor> FakePlatformSensorProvider::CreateSensorInternal(
+    mojom::SensorType type,
+    mojo::ScopedSharedBufferMapping mapping,
+    uint64_t buffer_size) {
+  return new FakePlatformSensor(type, std::move(mapping), buffer_size, this);
+}
+
+}  // namespace device