Use a ThreadChecker in DeviceSensorHost instead of DCHECK_CURRENTLY_ON.

content/browser/device_sensors/device_sensor_host.h

 // 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.
 
 #ifndef CONTENT_BROWSER_DEVICE_SENSORS_DEVICE_SENSOR_HOST_H_
 #define CONTENT_BROWSER_DEVICE_SENSORS_DEVICE_SENSOR_HOST_H_
 
 #include "base/macros.h"
 #include "base/memory/shared_memory.h"
 #include "content/browser/device_sensors/device_sensors_consts.h"
 #include "device/sensors/public/interfaces/light.mojom.h"
 #include "device/sensors/public/interfaces/motion.mojom.h"
 #include "device/sensors/public/interfaces/orientation.mojom.h"
 #include "mojo/public/cpp/bindings/interface_request.h"
 #include "mojo/public/cpp/bindings/strong_binding.h"
 
 namespace content {
 
 // A base class for device sensor related mojo interface implementations.
 template <typename MojoInterface, ConsumerType consumer_type>
 class DeviceSensorHost : public MojoInterface {
  public:
   static void Create(mojo::InterfaceRequest<MojoInterface> request);
 
   // All methods below to be called on the IO thread.

[timvolodine, 2016/07/20 18:41:56]

hmm I understand this is now actually enforced in render_process_host_impl.cc by
adding on io_task_runner. Can we at least add a corresponding dcheck somewhere
in create/construction of this host?

[Sam McNally, 2016/07/21 00:09:28]

Done.

   ~DeviceSensorHost() override;
 
  private:
   explicit DeviceSensorHost(mojo::InterfaceRequest<MojoInterface> request);
 
   void StartPolling(
       const typename MojoInterface::StartPollingCallback& callback) override;
   void StopPolling() override;
 
   bool is_started_;
 
   mojo::StrongBinding<MojoInterface> binding_;
 
+  base::ThreadChecker thread_checker_;
+
   DISALLOW_COPY_AND_ASSIGN(DeviceSensorHost);
 };
 
 using DeviceLightHost =
     DeviceSensorHost<device::mojom::LightSensor, CONSUMER_TYPE_LIGHT>;
 using DeviceMotionHost =
     DeviceSensorHost<device::mojom::MotionSensor, CONSUMER_TYPE_MOTION>;
 using DeviceOrientationHost = DeviceSensorHost<device::mojom::OrientationSensor,
                                                CONSUMER_TYPE_ORIENTATION>;
 using DeviceOrientationAbsoluteHost =
     DeviceSensorHost<device::mojom::OrientationAbsoluteSensor,
                      CONSUMER_TYPE_ORIENTATION_ABSOLUTE>;
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_DEVICE_SENSORS_DEVICE_SENSOR_HOST_H_