[sensors] Add a browser test to sanity check ambient light sensor.

device/generic_sensor/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 "device/generic_sensor/platform_sensor_provider.h"
+
+#if defined(OS_MACOSX)
+#include "device/generic_sensor/platform_sensor_provider_mac.h"
+#elif defined(OS_ANDROID)
+#include "device/generic_sensor/platform_sensor_provider_android.h"
+#endif
+
+namespace {
+
+static device::PlatformSensorProvider* g_provider_for_testing = nullptr;
+}
+
+namespace device {
+
+// static
+void PlatformSensorProvider::SetProviderForTesting(
+    PlatformSensorProvider* provider) {
+  g_provider_for_testing = provider;
+}
+
+// static
+PlatformSensorProvider* PlatformSensorProvider::GetInstance() {
+  if (g_provider_for_testing)
+    return g_provider_for_testing;
+#if defined(OS_MACOSX)
+  return PlatformSensorProviderMac::GetInstance();
+#elif defined(OS_ANDROID)
+  return PlatformSensorProviderAndroid::GetInstance();
+#else
+  return nullptr;
+#endif
+}
+
+}  // namespace device