Fix StatsCounters on mac.
Fix StatsCounters on mac.

In order for the shared memory to work, they must all use the same file name
which is keyed by the pid of the browser process. Previously the mac code path
was using the pid for each process so there was no sharing happening. Now mac
uses the same code path as win which properly uses the parent pid for all procs.

BUG=None
TEST=None

Review URL: http://codereview.chromium.org/6364006

git-svn-id: http://src.chromium.org/svn/trunk/src@72538 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 79d88273a31d7180d6bd30fc80dfcdacf28eeb11
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