[sensors] Ambient light sensor implementation for ChromeOS and Linux.

device/generic_sensor/platform_sensor_provider_base.h

Index: device/generic_sensor/platform_sensor_provider_base.h
diff --git a/device/generic_sensor/platform_sensor_provider_base.h b/device/generic_sensor/platform_sensor_provider_base.h
index a5da624c4f0e241e00c80110b3e45c72603ed7d8..b6c33b1e29b71daa56109fbee0d08119455f37a1 100644
--- a/device/generic_sensor/platform_sensor_provider_base.h
+++ b/device/generic_sensor/platform_sensor_provider_base.h
@@ -35,6 +35,11 @@ class DEVICE_GENERIC_SENSOR_EXPORT PlatformSensorProviderBase
   // alive; 'false' otherwise.
   bool HasSensors() const;
 
+  // Implementations might want to override this in order to be able
+  // to read from sensor files. For example, linux does so.
+  virtual void SetFileTaskRunner(
+      scoped_refptr<base::SingleThreadTaskRunner> file_task_runner) {}
+
  protected:
   PlatformSensorProviderBase();
   virtual ~PlatformSensorProviderBase();