Convert the OS_CHROMEOS-only zip creator IPC to use mojo rather
than IPC. Expose the mojo to the browser process using the mojo
utility process policy file. Update the client to call the mojo
service using a mojo utility client, remove all dependencies on
UtilityProcessHostClient. Add a new mojo utility client api:

  utility_process_mojo_client_->set_exposed_directory(dir)

to allow mojo utility clients to expose the target directory in
the utility process sandbox just like UtilityProcessHostClient.
Minor name changes, no abbrvs.

Now in chrome/utility/chrome_content_utility_client.cc continue
the saga of deleting the Send and ReleaseProcessIfNeeded helper
routines: make remaining users call these services directly and
remove the helpers. Add the mojo ZipFileCreatorImpl class.

Covered by existing tests: ZipFileCreatorTest.SomeFilesZip, per
https://codereview.chromium.org/2703463005

BUG=597124

Review-Url: https://codereview.chromium.org/2705613003
Cr-Commit-Position: refs/heads/master@{#453825}