[sensors](Linux) Fix tsan data race in sensor reader

device/generic_sensor/platform_sensor_linux.h

Index: device/generic_sensor/platform_sensor_linux.h
diff --git a/device/generic_sensor/platform_sensor_linux.h b/device/generic_sensor/platform_sensor_linux.h
index e8555d931ee1486401d85ed2f0f3a9a19baabf52..9442b0c0b61319c6a3582f54f33752ae8d3625f3 100644
--- a/device/generic_sensor/platform_sensor_linux.h
+++ b/device/generic_sensor/platform_sensor_linux.h
@@ -45,6 +45,8 @@ class PlatformSensorLinux : public PlatformSensor {
   const PlatformSensorConfiguration default_configuration_;
   const mojom::ReportingMode reporting_mode_;
 
+  scoped_refptr<base::SingleThreadTaskRunner> polling_thread_task_runner_;
+
   // A sensor reader that reads values from sensor files
   // and stores them to a SensorReading structure.
   std::unique_ptr<SensorReader> sensor_reader_;