Adds support for Google Developer Shell session credentials

[aalexand]

No description provided.

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[skelterjohn]

LGTM. regarding CLA, have you registered as a github googler?

[aalexand]

have you registered as a github googler?

I think I have now.

[googlebot]

CLAs look good, thanks!

[coveralls]

Coverage increased (+0.76%) to 64.72% when pulling 701abfd on aalexand:support-devshell-credentials into 07da0fe on google:master.

[coveralls]

Coverage increased (+0.76%) to 64.72% when pulling 0627984 on aalexand:support-devshell-credentials into 07da0fe on google:master.

[nathanielmanistaatgoogle]

(I'll be taking a look at this at some point.)

[nathanielmanistaatgoogle]

Please squash your commits.

[coveralls]

Coverage increased (+0.73%) to 64.68% when pulling c8eaffa on aalexand:support-devshell-credentials into 07da0fe on google:master.

[nathanielmanistaatgoogle]

I'm satisfied (thank you for the changes). Will anyone else be reviewing this before it goes in?

[skelterjohn]

changes LGTM as well. let me know if you consider this ready to merge.

[nathanielmanistaatgoogle]

I consider this ready to merge.

Last call for obstacles, blockers, and objections?

[aalexand]

I think it should be merged now.