Add ForceEphemeralProfiles policy.

Adds the policy and wires it into the Prefs.

BUG=298944
TEST=Unit tests pass.
R=joaodasilva@chromium.org

Review URL: https://codereview.chromium.org/24763002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225971 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 225971
Remove deprecated usage of FromWStringHack() from importer and flush_cache.

BUG=76112
TEST=compiles, no functional changes.
R=thestig, isherman

Review URL: https://codereview.chromium.org/25174002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225972 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 225972