mojo_run: infer --origin from `MOJO_VERSION` file if present.

mojo_run: infer --origin from `MOJO_VERSION` file if present.

This allows mojo consumers that use pinned mojo version not to set
--origin to point to the correct google storage directory manually - it
will be set based on MOJO_VERSION if MOJO_VERSION is present AND
--origin is not passed explicitly.

R=tonyg@chromium.org

Committed: https://chromium.googlesource.com/external/mojo/+/d34ebee9950ba27b50ef8f78d29c2bb3e6d6dc51

[ppi, 2016-01-13 14:11:12]

ppi@chromium.org changed reviewers:
+ qsr@chromium.org, tonyg@chromium.org

[ppi, 2016-01-13 14:11:12]

Hi Ben or Tony,

ptal.

[tonyg, 2016-01-13 14:38:05]

Good idea, this lgtm

A couple of thoughts though:
1. It'd be nice if the usage string showed this as the default value for the
argument (or at least mentioned it if it is hard to plumb that).
2. This should probably be documented in the README

[ppi, 2016-01-13 16:44:30]

Thanks, Tony! The default origin value is calculated at runtime (depends on
whether we run on Android or Linux). Added documentation to arg help and README.

[ppi, 2016-01-13 16:48:01]

Also added a --verbose printout to facilitate debugging, e.g.:

  "Inferring origin from `MOJO_VERSION` as:
https://storage.googleapis.com/mojo/services/android-arm/f9e73ad5730fbd29e312...

[ppi, 2016-01-13 16:48:25]

Description was changed from

==========
mojo_run: infer --origin from `MOJO_VERSION` file if present.

This allows mojo consumers that use pinned mojo version not to set
--origin to point to the correct google storage directory manually - it
will be set based on MOJO_VERSION if MOJO_VERSION is present AND
--origin is not passed explicitly.
==========

to

==========
mojo_run: infer --origin from `MOJO_VERSION` file if present.

This allows mojo consumers that use pinned mojo version not to set
--origin to point to the correct google storage directory manually - it
will be set based on MOJO_VERSION if MOJO_VERSION is present AND
--origin is not passed explicitly.

R=tonyg@chromium.org

Committed:
https://chromium.googlesource.com/external/mojo/+/d34ebee9950ba27b50ef8f78d29...
==========

[ppi, 2016-01-13 16:48:27]

Committed patchset #3 (id:40001) manually as
d34ebee9950ba27b50ef8f78d29c2bb3e6d6dc51 (presubmit successful).