Linux: Pass --user-data-dir to the Zygote. (Reland r41369 now that the directory creation race has been fixed.)
Linux: Pass --user-data-dir to the Zygote. (Reland r41369 now that the directory creation race has been fixed.)

BUG=none
TEST=On Linux, "chrome --enable-logging --user-data-dir=/tmp/foobar" writes renderer logs to chrome_debug.log in /tmp/foobar rather than in $XDG_CONFIG_HOME.

TBR=evan
Original review: http://codereview.chromium.org/885003
Review URL: http://codereview.chromium.org/1060002

git-svn-id: http://src.chromium.org/svn/trunk/src@41891 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: a55fffff3601957b44bf6ecf93809c928749b9d4
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser