Remove content::BrowserThread knowledge from Device Sensors

content/browser/device_sensors/device_sensor_service.h

Index: content/browser/device_sensors/device_sensor_service.h
diff --git a/content/browser/device_sensors/device_sensor_service.h b/content/browser/device_sensors/device_sensor_service.h
index 00946b484ae160a329029147e4255bf3a4dd2d63..424f2706a24852da3b7f0ef54d76cbb1e02b50cf 100644
--- a/content/browser/device_sensors/device_sensor_service.h
+++ b/content/browser/device_sensors/device_sensor_service.h
@@ -30,19 +30,20 @@ class CONTENT_EXPORT DeviceSensorService {
 
   // Increments the number of users of the provider. The Provider is running
   // when there's > 0 users, and is paused when the count drops to 0.
-  // Must be called on the I/O thread.
+  // Must be called on a thread that can perform I/O.
   void AddConsumer(ConsumerType consumer_type);
 
   // Removes a consumer. Should be matched with an AddConsumer call.
-  // Must be called on the I/O thread.
+  // Must be called on a thread that can perform I/O.
   void RemoveConsumer(ConsumerType cosumer_type);
 
   // Returns the shared memory handle of the device motion data.
   mojo::ScopedSharedBufferHandle GetSharedMemoryHandle(
       ConsumerType consumer_type);
 
-  // Stop/join with the background polling thread in |provider_|.
-  void Shutdown();
+  // Stop/join with the background polling thread in |provider_|. Must be
+  // called on the UI thread.
+  void ShutDownOnUIThread();
 
   // Injects a custom data fetcher for testing purposes. This class takes
   // ownership of the injected object.
@@ -63,7 +64,9 @@ class CONTENT_EXPORT DeviceSensorService {
   int num_orientation_absolute_readers_;
   bool is_shutdown_;
   std::unique_ptr<DataFetcherSharedMemory> data_fetcher_;
-  base::ThreadChecker thread_checker_;
+
+  // Associated with the IO thread.
+  base::ThreadChecker io_thread_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(DeviceSensorService);
 };