Add API to CommandLine to get a FilePath value of a switch.
Add API to CommandLine to get a FilePath value of a switch.

This is the last piece needed before I can clean up all the callers.

BUG=24672
TEST=compiles

Review URL: http://codereview.chromium.org/274022

git-svn-id: http://src.chromium.org/svn/trunk/src@28876 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 69cd0b339fc001cf0b90bcc6875c2eece40d792a
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