Roll tools/swarming_client/ to a57d7db4026bca8e0fab9aadd4953503e8d74e74.

Roll tools/swarming_client/ to a57d7db4026bca8e0fab9aadd4953503e8d74e74.

$ git log f9e401bab..a57d7db40 --date=short --format='%ad %ae %s' | sed 's/@chromium\.org//'
2014-10-15 maruel Add --cache to isolateserver.py download.
2014-10-15 maruel Preparation work to enable isolateserver.py download to use a local cache.

TBR=vadimsh@chromium.org
BUG=

Committed: https://crrev.com/d49dfe824ed34f647dff72d5d8012edd490bfd39
Cr-Commit-Position: refs/heads/master@{#300023}

[M-A Ruel, 2014-10-16 23:41:10]

TBR'ing, it's not a tricky roll.

[M-A Ruel, 2014-10-16 23:41:14]

The CQ bit was checked by maruel@chromium.org

[commit-bot: I haz the power, 2014-10-16 23:44:07]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/664493002/1

[commit-bot: I haz the power, 2014-10-17 00:18:23]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-10-17 00:19:01]

Patchset 1 (id:??) landed as
https://crrev.com/d49dfe824ed34f647dff72d5d8012edd490bfd39
Cr-Commit-Position: refs/heads/master@{#300023}