Fix webkit_unit_tests.isolate to use ' instead of ".

Fix webkit_unit_tests.isolate to use ' instead of ".

Double quotes cause isolate.go to choke with the following error:

webkit_unit_tests  failed to process isolate (isolateDir: /usr/local/google/home/joelo/src/chromium/src/third_party/WebKit/Source/web): invalid character '\\' looking for beginning of value

BUG=524758, 531819
TBR=dpranke@chromium.org,maruel@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=202495

[joelo, 2015-09-17 22:03:43]

joelo@chromium.org changed reviewers:
+ dpranke@chromium.org, maruel@chromium.org

[joelo, 2015-09-17 22:04:17]

The CQ bit was checked by joelo@chromium.org

[commit-bot: I haz the power, 2015-09-17 22:04:43]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1352923003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1352923003/1

[commit-bot: I haz the power, 2015-09-17 23:45:39]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-09-17 23:45:39]

Try jobs failed on following builders:
  linux_android_rel_ng on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_android_r...)

[joelo, 2015-09-18 01:37:26]

The CQ bit was checked by joelo@chromium.org

[commit-bot: I haz the power, 2015-09-18 01:37:51]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1352923003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1352923003/1

[commit-bot: I haz the power, 2015-09-18 03:02:52]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=202495