Allow specification of the version file for download_shell_binary to use.

Allow specification of the version file for download_shell_binary to use.

download_shell_binary.py assumes the presence of a //mojo/public/VERSION file
that contains the SHA1 corresponding to the shell version to fetch. However,
this file is not present in the Mojo repo, and hence not present in the SDK
mirror. This CL allows the client of download_shell_binary.py to specify the
path to the version file to allow maintaining the version file outside of the
SDK itself when using the mirror.

R=jamesr@chromium.org

Committed: https://chromium.googlesource.com/external/mojo/+/6a6cc936c631fedd2c23022e49d6ed1969e6965a

[blundell, 2015-02-23 15:51:22]

blundell@chromium.org changed reviewers:
+ jamesr@chromium.org

[blundell, 2015-02-23 15:51:22]

Hi James,

I realized that the approach of obtaining the shell version to fetch from the
"Cr-Mirrored-Commit" line in the mirror has a flaw: the shell version won't be
rolled until there is a new commit to the SDK. There could be an arbitrarily
long gap between a consumer needing a new shell version (e.g., due to a feature
enhancement or bugfix) and there being a commit to the SDK in the Mojo repo.

This CL simply lets consumers maintain the version file outside of the mirror.

[jamesr, 2015-02-23 19:09:53]

lgtm

[blundell, 2015-02-24 09:10:26]

Committed patchset #1 (id:1) manually as
6a6cc936c631fedd2c23022e49d6ed1969e6965a (presubmit successful).