Refactor TranslateAcceptLanguages as a BrowserContextKeyedService
This CL refactors TranslateAcceptLanguages as a BrowserContextKeyedService,
and moves it into the Translate component.
The choice of BrowserContextKeyedService seems obvious since there is one
accept languages list per profile.
The existing code is simplified, since the handling of profiles and notifications
is deferred to the BrowserContextKeyedService code and can be removed.
Note that there is now one TranslateAcceptLanguages instance per profile (it
was a singleton owned by TranslateManager previously).
BUG=335076
Review URL: https://codereview.chromium.org/
149753006
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@250480 0039d316-1c4b-4281-b951-d872f2087c98