[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..0a6ce3728f00c933ca3bba378edbac7d236f5906 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 make it
+  // possible to destroy own threads without a crash.
+  virtual void SetTaskRunner(
+      scoped_refptr<base::SingleThreadTaskRunner> task_runner) {}
+
  protected:
   PlatformSensorProviderBase();
   virtual ~PlatformSensorProviderBase();