Use --gtest_flagfile for --gtest_filter in unit test launcher

Use --gtest_flagfile for --gtest_filter in unit test launcher

This should help with exceeding command line length limits
with long filter strings when running a lot of tests
in the same batch.

BUG=509883
Committed: https://crrev.com/d6c9c836e856b3d223747464f82b5586778ffc73
Cr-Commit-Position: refs/heads/master@{#356941}

[Paweł Hajdan Jr., 2015-10-29 12:31:43]

phajdan.jr@chromium.org changed reviewers:
+ sky@chromium.org

[Jamie Madill, 2015-10-29 16:06:26]

jmadill@chromium.org changed reviewers:
+ jmadill@chromium.org

[Jamie Madill, 2015-10-29 16:06:26]

I tested this CL locally with angle_deqp_gles2_tests and a patch to give them
much longer names, and a batch size of 2000. It worked correctly.

[sky, 2015-10-29 17:32:34]

LGTM assuming the builders still show the tests being run.

https://codereview.chromium.org/1430633002/diff/20001/base/test/launcher/unit...
File base/test/launcher/unit_test_launcher.cc (right):

https://codereview.chromium.org/1430633002/diff/20001/base/test/launcher/unit...
base/test/launcher/unit_test_launcher.cc:116: if (!temp_dir_.IsValid()) {
nit: no {}. That said, I would likely move this into the CHECK, eg:

CHECK(temp_dir_.IsValid() || temp_dir_.CreateUniqueTempDir());

[Paweł Hajdan Jr., 2015-10-29 18:43:20]

https://codereview.chromium.org/1430633002/diff/20001/base/test/launcher/unit...
File base/test/launcher/unit_test_launcher.cc (right):

https://codereview.chromium.org/1430633002/diff/20001/base/test/launcher/unit...
base/test/launcher/unit_test_launcher.cc:116: if (!temp_dir_.IsValid()) {
On 2015/10/29 at 17:32:34, sky wrote:
> nit: no {}. That said, I would likely move this into the CHECK, eg:
> 
> CHECK(temp_dir_.IsValid() || temp_dir_.CreateUniqueTempDir());

Done.

[Paweł Hajdan Jr., 2015-10-29 18:43:22]

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

[Paweł Hajdan Jr., 2015-10-29 18:43:23]

The patchset sent to the CQ was uploaded after l-g-t-m from sky@chromium.org
Link to the patchset: https://codereview.chromium.org/1430633002/#ps40001
(title: "nit")

[commit-bot: I haz the power, 2015-10-29 18:44:18]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1430633002/40001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1430633002/40001

[commit-bot: I haz the power, 2015-10-29 20:56:02]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-10-29 20:57:16]

Patchset 3 (id:??) landed as
https://crrev.com/d6c9c836e856b3d223747464f82b5586778ffc73
Cr-Commit-Position: refs/heads/master@{#356941}