Componentize SigninManagerCookieHelper.

This CL eliminates content::BrowserThread dependencies from
SigninManagerCookieHelper by injecting the required threads. It additionally
moves SigninManagerCookieHelper into //components/signin.

BUG=334206
TBR=joi

Review URL: https://codereview.chromium.org/135183004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245955 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 245955