Linux: Allow IO in ProcessMetrics::GetWorkingSetKBytes().
Linux: Allow IO in ProcessMetrics::GetWorkingSetKBytes().

BUG=61340
TEST=Opening up the task manager on Linux in debug mode does not assert.
Review URL: http://codereview.chromium.org/5928001

git-svn-id: http://src.chromium.org/svn/trunk/src@69331 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 0bb839072b3586b76e7bdb85d55f6aeddb4b2e8a
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