Fix problem with crash_sender being able to run multiple times concurrently.

Fix problem with crash_sender being able to run multiple times concurrently.

BUG=6134
TEST=Run CrashSender and UserCrash, also test starting those tests while crash_sender is already running.

Change-Id: Ie80c450f6b0da1b67398aa67fd9b74903abc430b

[petkov-google, 2010-08-26 23:09:21]

LGTM but you still have a race, right? If you start two processes in parallel
and they go through the check_not_already_running check successfully, they will
both try to run in parallel... Maybe this CL makes that less likely to happen
but it doesn't really fix the issue completely.

[petkov, 2010-08-26 23:11:29]

On 2010/08/26 23:09:21, petkov-google wrote:
> LGTM but you still have a race, right? If you start two processes in parallel
> and they go through the check_not_already_running check successfully, they
will
> both try to run in parallel... Maybe this CL makes that less likely to happen
> but it doesn't really fix the issue completely.

[petkov, 2010-08-27 00:55:00]

See below.

http://codereview.chromium.org/3197024/diff/5001/6001
File crash_sender (right):

http://codereview.chromium.org/3197024/diff/5001/6001#newcode82
crash_sender:82: echo $$ > "${RUN_FILE}"
You still have a race here.

[petkov, 2010-08-27 01:00:55]

LGTM based on discussion (maybe add a comment).