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: dd90618784b6a4b323ea0c23a071cb1c9e6f2ac7@41891 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser