Move KWalletDBus util from the Password Manager to OSCrypt.

This is part of deprecating the use of OS services for
storing passwords with Password Manager.

The moved util will be used to create a specialization of
KeyStorage for KWallet.

BUG=602624

TBR=davidben@chromium.org

Review-Url: https://codereview.chromium.org/2086123003
Cr-Commit-Position: refs/heads/master@{#401836}
10 files changed