Move Password(Generation)Manager IPC reception to ContentPasswordDriver

This CL exposes the methods that PasswordManager and PasswordGenerationManager
use in response to IPC as public APIs on those classes, and moves the IPC
handling into ContentPasswordDriver.

BUG=340669, 340690
NOTRY=true

Review URL: https://codereview.chromium.org/136093012

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249325 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 249325