Prevent potential NULL-dereferences in ResetProfileSettingsHandler for off-the-record profiles (which is the case in ChromeOS Guest mode).

BUG=330337
TBR=bauerb@chromium.org

Review URL: https://codereview.chromium.org/118423005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242413 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 242413