Fix v8rel script after adding roll branches.

Fix v8rel script after adding roll branches.

Use git hashes as keys when referring to releases, not
pure commit position numbers as those are not unique.

Better bailout to only check for recent releases.

Add new branching method with a roll branch in heads to
the v8rel test case.

Fix the way v8 is referred to in DEPS files in the test
cases. The test still had svn-number style.

BUG=chromium:451975
TBR=tandrii@chromium.org
NOTRY=true
LOG=n

TEST=./script_test.py

Committed: https://crrev.com/b351e3020fadad986b965d8e3300d83088e64c38
Cr-Commit-Position: refs/heads/master@{#26669}

[Michael Achenbach, 2015-02-16 14:51:06]

machenbach@chromium.org changed reviewers:
+ tandrii@chromium.org

[Michael Achenbach, 2015-02-16 14:58:49]

PTAL

[tandrii(chromium), 2015-02-16 15:31:06]

LGTM with 1 nit

https://codereview.chromium.org/928243002/diff/20001/tools/release/releases.py
File tools/release/releases.py (right):

https://codereview.chromium.org/928243002/diff/20001/tools/release/releases.p...
tools/release/releases.py:433: 
nit: del extra space?

[Michael Achenbach, 2015-02-16 16:40:07]

New patchsets have been uploaded after l-g-t-m from tandrii@chromium.org

[Michael Achenbach, 2015-02-16 16:40:38]

Done

[Michael Achenbach, 2015-02-16 16:51:38]

Patch 4 fixes an error in the test. The chromium release retrieval should go
backwards until it finds an unknown v8 revisions and then stop.

[Michael Achenbach, 2015-02-16 16:51:47]

The CQ bit was checked by machenbach@chromium.org

[commit-bot: I haz the power, 2015-02-16 16:52:48]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/928243002/60001

[commit-bot: I haz the power, 2015-02-16 17:00:51]

Committed patchset #4 (id:60001)

[commit-bot: I haz the power, 2015-02-16 17:01:07]

Patchset 4 (id:??) landed as
https://crrev.com/b351e3020fadad986b965d8e3300d83088e64c38
Cr-Commit-Position: refs/heads/master@{#26669}