Componentize SigninManager.

This CL does the following:

- Componentizes SigninIdAccountHelper, on which SigninManager depends
- Abstracts SigninManager's (embedder-level) calculation of whether to merge
  signin credentials into the cookie jar via SigninClient
- Eliminates the |profile| argument of SigninManagerBase::Initialize() now that
  SigninManager no longer needs it
- Componentizes SigninManager

BUG=334209,333998
TBR=thakis

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=260636

Review URL: https://codereview.chromium.org/218713002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@260831 0039d316-1c4b-4281-b951-d872f2087c98
138 files changed