Keeping golden screenshots in Google Storage

Now golden screenshots are kept in Google Storage. To download them automatically, a hook should be added to .gclient. Specifying directories for golden screenshots and artifacts is optional now. There is also a python script that should be run to update screenshots in Google Storage after using update mode.

BUG=395653
Committed: https://crrev.com/340cab2eadc16dd1ef0e9c4295dbaa28e61c4073
Cr-Commit-Position: refs/heads/master@{#299109}

[Lisa Ignatyeva, 2014-10-09 18:16:47]

elizavetai@chromium.org changed reviewers:
+ antrim@chromium.org

[Denis Kuznetsov (DE-MUC), 2014-10-10 09:25:09]

I don't like hard-coded default paths for golden screenshots / artifacts,
especially having them under project tree.
They both should be specified via command-line, with tests failing if there
should be path (for this mode), but it is not specified.
Same is true for utility.
Also make sure that relative paths have correct root to evaluate (e.g. that
update utility can be run with current path /etc).

[Lisa Ignatyeva, 2014-10-10 12:28:46]

Fixed that.

[Denis Kuznetsov (DE-MUC), 2014-10-10 12:56:03]

lgtm

[Lisa Ignatyeva, 2014-10-10 12:56:16]

The CQ bit was checked by elizavetai@chromium.org

[commit-bot: I haz the power, 2014-10-10 12:57:23]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/639283004/120001

[commit-bot: I haz the power, 2014-10-10 13:04:52]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-10-10 13:04:53]

Try jobs failed on following builders:
  chromium_presubmit on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/chromium_presub...)

[Lisa Ignatyeva, 2014-10-10 13:24:20]

The CQ bit was checked by elizavetai@chromium.org

[commit-bot: I haz the power, 2014-10-10 13:24:34]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/639283004/320001

[commit-bot: I haz the power, 2014-10-10 14:04:36]

Committed patchset #4 (id:320001)

[commit-bot: I haz the power, 2014-10-10 14:05:25]

Patchset 4 (id:??) landed as
https://crrev.com/340cab2eadc16dd1ef0e9c4295dbaa28e61c4073
Cr-Commit-Position: refs/heads/master@{#299109}