Refactor native_backend_kwallet_x

Parts of the implementation have been moved into a new util, KWalletDBus.
The purpose of this is to make those pieces of code reusable, so that the
(upcoming) KWallet implementation of OSCrypt can use them and avoid code
duplication.

BUG=602624

Review-Url: https://codereview.chromium.org/2057123002
Cr-Commit-Position: refs/heads/master@{#401245}
7 files changed