Clean up the way we determine which env vars to pass to content_shell.

Clean up the way we determine which env vars to pass to content_shell.

We were passing more variables across than necessary, duplicating some
work, and things were generally unclear. This patch consolidates most
of the logic and makes things clearer.

R=ojan@chromium.org
BUG=

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=156355

[Dirk Pranke, 2013-08-19 21:58:52]

https://codereview.chromium.org/22978015/diff/1/Tools/Scripts/webkitpy/layout...
File Tools/Scripts/webkitpy/layout_tests/port/base.py (right):

https://codereview.chromium.org/22978015/diff/1/Tools/Scripts/webkitpy/layout...
Tools/Scripts/webkitpy/layout_tests/port/base.py:877: 'WEBKITOUTPUTDIR',   #
FIXME: Is this still used?
Note that I don't want to actually try and figure out the answer to these FIXME
questions as part of this patch ...

[ojan, 2013-08-19 22:09:50]

lgtm

[commit-bot: I haz the power, 2013-08-19 22:10:00]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/dpranke@chromium.org/22978015/1

[commit-bot: I haz the power, 2013-08-20 01:12:29]

Retried try job too often on mac_blink_rel for step(s) webkit_tests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=mac_blink_...

[Dirk Pranke, 2013-08-20 01:28:12]

Committed patchset #1 manually as r156355 (presubmit successful).