I think we don't need to move the interfaces into //services/device/public in the patch for this CL. Because doing so will bring dependency from //device/sensors onto //services.
The interfaces and cpp client library will be moved into //services together with other files of //device/sensors.  

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/57f4387cd58afa6949c3fa158271d49690ca8d81

commit 57f4387cd58afa6949c3fa158271d49690ca8d81
Author: ke.he <ke.he@intel.com>
Date: Thu Mar 23 07:40:03 2017

Port device_sensors to be hosted in Device Service

This patch moves device_sensors to be hosted by the Device Service.
Before this patch, device_sensors were registered in RenderProcessHostImpl, the
function DeviceSensorHost::Create() which makes StrongBinding is run on IO
Thread(if Android platform) or UI thread(if other platforms).

In this patch, we add a member |io_task_runner_| in DeviceService and use
PostTask() to make sure the StrongBindings still happen in same threads as
before.

TODO: The mojom and cpp library are still in //device/sensors, will move them
into //services/device later (when move //device/sensors/ implementations into
//service).

BUG= 686706 
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_site_isolation

Review-Url: https://codereview.chromium.org/2692993006
Cr-Commit-Position: refs/heads/master@{#459015}

[modify] https://crrev.com/57f4387cd58afa6949c3fa158271d49690ca8d81/content/browser/BUILD.gn
[modify] https://crrev.com/57f4387cd58afa6949c3fa158271d49690ca8d81/content/browser/renderer_host/render_process_host_impl.cc
[modify] https://crrev.com/57f4387cd58afa6949c3fa158271d49690ca8d81/content/public/app/mojo/content_browser_manifest.json
[modify] https://crrev.com/57f4387cd58afa6949c3fa158271d49690ca8d81/content/public/app/mojo/content_renderer_manifest.json
[modify] https://crrev.com/57f4387cd58afa6949c3fa158271d49690ca8d81/content/renderer/BUILD.gn
[modify] https://crrev.com/57f4387cd58afa6949c3fa158271d49690ca8d81/content/renderer/device_sensors/device_sensor_event_pump.h
[modify] https://crrev.com/57f4387cd58afa6949c3fa158271d49690ca8d81/content/test/BUILD.gn
[modify] https://crrev.com/57f4387cd58afa6949c3fa158271d49690ca8d81/services/device/BUILD.gn
[modify] https://crrev.com/57f4387cd58afa6949c3fa158271d49690ca8d81/services/device/device_service.cc
[modify] https://crrev.com/57f4387cd58afa6949c3fa158271d49690ca8d81/services/device/device_service.h
[modify] https://crrev.com/57f4387cd58afa6949c3fa158271d49690ca8d81/services/device/manifest.json