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This service doesn't need any Chrome dependencies after all and so it
can move into //extensions. This will make it possible for the USB
extensions API code to directly depend on it. In the process I have
rewritten the service with a couple improvements:

* C++11 for-each loops are used instead of explicit iterators.
* The DevicePermissions object is no longer an inner class (so it can
  be forward declared) and it is explicitly copied when requested so
  that the ownership of data on the FILE and UI threads is clear.

BUG=

Review URL: https://codereview.chromium.org/606503002

Cr-Commit-Position: refs/heads/master@{#297230}