Revert "Use Xvfb in isolated testing only if use_x11 is set"

Revert "Use Xvfb in isolated testing only if use_x11 is set"

This reverts commit 8a7be0714892c0c6360c45d0d602c119873b468e.

We've been seeing a problem with tab_capture_end2end_tests
taking too much time on linux_gpu_triggered_tests (over 1 hour
as opposed to below 30 seconds).

This was traced to wrong command on the isolate server,
as can be seen e.g. with [1] (good) and [2] (bad).

From builder history I was able to narrow down suspect revision range to just
cafcab99f5ea (good) [3] and 8a7be0714892 (bad) [4].

There are only two CLs in that range, https://codereview.chromium.org/841693004
and https://codereview.chromium.org/813363003 . First one is just a histogram
description change, while the latter changes *.isolate files, which is much more
suspect.

[1] https://isolateserver.appspot.com/browse?namespace=default-gzip&hash=13030c2ece3e5467ba858a978c685865181d32a6
[2] https://isolateserver.appspot.com/browse?namespace=default-gzip&hash=104dec9bff0fc701eac105a80d7d64be5b43b033
[3] http://build.chromium.org/p/tryserver.chromium.gpu/builders/linux_gpu_triggered_tests/builds/97223
[4] http://build.chromium.org/p/tryserver.chromium.gpu/builders/linux_gpu_triggered_tests/builds/97224

TBR=spang
BUG=440882
Committed: https://chromium.googlesource.com/chromium/src/+/99ef9b4892ce79eef6f758cad66de092a72e9bc1

[commit-bot: I haz the power, 2015-01-08 09:35:42]

Patchset 1 (id:??) landed as
https://crrev.com/99ef9b4892ce79eef6f758cad66de092a72e9bc1
Cr-Commit-Position: refs/heads/master@{#310464}

[Paweł Hajdan Jr., 2015-01-08 09:35:45]

Committed patchset #1 (id:1) manually as
99ef9b4892ce79eef6f758cad66de092a72e9bc1 (presubmit successful).

[Paweł Hajdan Jr., 2015-01-08 09:36:07]

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

[Paweł Hajdan Jr., 2015-01-08 09:36:07]

TBR

[Paweł Hajdan Jr., 2015-01-08 10:18:19]

FWIW this revert seems to have helped, see e.g.
http://build.chromium.org/p/tryserver.chromium.gpu/builders/linux_gpu_trigger...