Drop 64 character limit in DeviceManagementRequest |agent| parameter

Drop 64 character limit in DeviceManagementRequest |agent| parameter

The HTTP POST |agent| parameter sent with a DeviceManagementRequest is
limited to 64 characters. After the git migration, Chrome includes its
git revision in the |agent|, making it longer than 64 characters.

This CL removes the arbitrary 64 character limit. This solution should be
considered temporary, until we have verified that the DMServer can handle
|agents| longer than 64 characters. If not, we will restore this limit and
change the construction of the string so that it never exceeds 64
characters.

BUG=406948
TEST=Browser tests no longer fail when the |agent| string is too long

Committed: https://crrev.com/a4b8fb8fdb4580f847e54e1e59419aa8182809e7
Cr-Commit-Position: refs/heads/master@{#291672}

[bartfab (slow), 2014-08-25 09:45:37]

Hi Joao,

Could you take a look? This will de-flake the tests. I started a thread with Bin
in parallel to figure out whether this is actually OK with DMServer too.

[Joao da Silva, 2014-08-25 11:36:03]

lgtm

[bartfab (slow), 2014-08-25 11:45:12]

The CQ bit was checked by bartfab@chromium.org

[commit-bot: I haz the power, 2014-08-25 11:45:27]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/bartfab@chromium.org/500013002/1

[commit-bot: I haz the power, 2014-08-25 12:37:43]

Committed patchset #1 (1) as 9ff894fcfee224effd2ecd5421ec851ede32efba

[commit-bot: I haz the power, 2014-09-10 02:34:11]

Patchset 1 (id:??) landed as
https://crrev.com/a4b8fb8fdb4580f847e54e1e59419aa8182809e7
Cr-Commit-Position: refs/heads/master@{#291672}