background_sync implements [1] by having:

1. background_sync related idl files and associated code are in //third_party/WebKit/Source/modules/background_sync

2. //third_party/WebKit/public/platform/modules/background_sync/WebSyncProvider.h
implemented in
//content/child/background_sync/*

3 - a service running in browser at
//content/browser/background_sync/background_sync_service_impl.*
and implementing background_sync_service.mojom.

This bug as part of Onion Soup project tracks removal of [2] by addressing the mojom channel directly from //third_party/WebKit/Source/modules/background_sync.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/30a0e93e8d121381d3674db975ba7ac7838ec7cf

commit 30a0e93e8d121381d3674db975ba7ac7838ec7cf
Author: juncai <juncai@chromium.org>
Date: Wed May 11 00:09:51 2016

[OnionSoup] Move background_sync.mojom from //content to
//third_party/WebKit

This patch is the first step of moving
background_sync.mojom from //content to //third_party/WebKit

BUG= 610374 

Review-Url: https://codereview.chromium.org/1960843002
Cr-Commit-Position: refs/heads/master@{#392779}

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[modify] https://crrev.com/30a0e93e8d121381d3674db975ba7ac7838ec7cf/content/content_common_mojo_bindings.gyp
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[modify] https://crrev.com/30a0e93e8d121381d3674db975ba7ac7838ec7cf/third_party/WebKit/public/platform/modules/serviceworker/OWNERS
[rename] https://crrev.com/30a0e93e8d121381d3674db975ba7ac7838ec7cf/third_party/WebKit/public/platform/modules/serviceworker/service_worker_event_status.mojom

Renaming Blink>Architecture to Blink>Internals

adithyas@ is working on moving background_sync in  bug 662134