Add CurrentProcessInfo::CreationTime() for Linux

This is used to measure startup performance.

BUG=None

Review URL: https://chromiumcodereview.appspot.com/21302005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@216409 0039d316-1c4b-4281-b951-d872f2087c98
12 files changed