Create PasswordManager component

This CL creates the PasswordManager component and moves a leaf file needed as
part of unit test support into it.

BUG=334616,334637
TBR=zea

Review URL: https://codereview.chromium.org/148383003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247771 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247771