Support disabling unit test batching. Use it for angle_end2end_tests

Support disabling unit test batching. Use it for angle_end2end_tests

This speeds up angle_end2end_tests 48s -> 12s on my Linux machine (4x).

BUG=501604
Committed: https://crrev.com/915c316c3431e193be1b025c557b5eee557e22d0
Cr-Commit-Position: refs/heads/master@{#336546}

[Paweł Hajdan Jr., 2015-06-26 13:38:45]

phajdan.jr@chromium.org changed reviewers:
+ kbr@chromium.org, piman@chromium.org, sky@chromium.org

[Paweł Hajdan Jr., 2015-06-26 13:38:45]

See https://codereview.chromium.org/1201583002 for context.

[Ken Russell (switch to Gerrit), 2015-06-26 15:38:09]

Thank you for adding this support. LGTM

We'll make the same change to all of the harnesses in that directory which
invoke ANGLE tests.

[piman, 2015-06-27 01:31:43]

lgtm

[Paweł Hajdan Jr., 2015-06-29 10:46:23]

The CQ bit was checked by phajdan.jr@chromium.org

[commit-bot: I haz the power, 2015-06-29 10:46:27]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1209243004/1

[commit-bot: I haz the power, 2015-06-29 11:49:26]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-29 11:50:23]

Patchset 1 (id:??) landed as
https://crrev.com/915c316c3431e193be1b025c557b5eee557e22d0
Cr-Commit-Position: refs/heads/master@{#336546}

[Geoff Lang, 2015-06-29 13:24:52]

It looks like this is causing angle_end2end_tests to fail on the Windows GPU FYI
bots.

[Stephen White, 2015-06-29 17:41:48]

On 2015/06/29 13:24:52, Geoff Lang wrote:
> It looks like this is causing angle_end2end_tests to fail on the Windows GPU
FYI
> bots.

Note: this patch was reverted in
https://chromium.googlesource.com/chromium/src.git/+/9dbed546384c617954e36ac7...
aka r336559 due to the above.