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

device/generic_sensor/platform_sensor_provider.h

Index: device/generic_sensor/platform_sensor_provider.h
diff --git a/device/generic_sensor/platform_sensor_provider.h b/device/generic_sensor/platform_sensor_provider.h
index ea6d3f5dae769a7a988f1bc9e543229cbdf8cce0..69007346891ebc3f22af80010fecaa167d09b9a8 100644
--- a/device/generic_sensor/platform_sensor_provider.h
+++ b/device/generic_sensor/platform_sensor_provider.h
@@ -20,6 +20,11 @@ class DEVICE_GENERIC_SENSOR_EXPORT PlatformSensorProvider
   // the current platform.
   static PlatformSensorProvider* GetInstance();
 
+  // This method allows to set a provider for testing and therefore
+  // skip the default platform provider. This allows testing without
+  // relying on the platform provider.
+  static void SetProviderForTesting(PlatformSensorProvider* provider);
+
  protected:
   PlatformSensorProvider() = default;
   ~PlatformSensorProvider() override = default;