Reland Auto-generate v8 version based on tags.

Reland Auto-generate v8 version based on tags.

This relands the CL
https://codereview.chromium.org/797503007/.

It runs the version generation two times. First during
runhooks as a fallback for recipes that loose git context
(e.g. android_aosp). Second during compilation like in the
original CL. In case of failures, the result from the
runhooks call will be reused.

BUG=chromium:446166
LOG=n

Committed: https://crrev.com/d3d6e38b2cba73b52bd5ed00f4441a7db3284a19
Cr-Commit-Position: refs/heads/master@{#26120}

[Michael Achenbach, 2015-01-15 13:34:26]

machenbach@chromium.org changed reviewers:
+ jkummerow@chromium.org, jochen@chromium.org, tandrii@chromium.org

[Michael Achenbach, 2015-01-15 13:38:24]

PTAL

[jochen (gone - plz use gerrit), 2015-01-16 10:46:53]

lgtm

[Michael Achenbach, 2015-01-18 10:58:24]

The CQ bit was checked by machenbach@chromium.org

[commit-bot: I haz the power, 2015-01-18 10:58:34]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/843913009/1

[commit-bot: I haz the power, 2015-01-18 11:25:49]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-01-18 11:26:13]

Patchset 1 (id:??) landed as
https://crrev.com/d3d6e38b2cba73b52bd5ed00f4441a7db3284a19
Cr-Commit-Position: refs/heads/master@{#26120}

[Michael Achenbach, 2015-01-18 15:42:09]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/855263002/ by machenbach@chromium.org.

The reason for reverting is: The gclient hook of v8 is not executed on this
builder:

http://build.chromium.org/p/tryserver.chromium.linux/builders/android_aosp/bu....