ChromeOS: Remove MockDBusThreadManager.

- Extends FakeDBusThreadManager about DBusClient setters.
- Removes default initialization of DBusClients from FakeDBusThreadManager.
- Replaces all occurrences of MockDBusThreadManager in tests by FakeDBusThreadManager.
- Every test now creates exactly the DBusClients that are required.
- Removes all references to Fake/Stub implementations from the DBusThreadManagerImpl used for production.

Depends on:
https://codereview.chromium.org/50243005/

BUG=275286
TBR=miket@chromium.org,mkwst@chromium.org,rtenneti@chromium.org

Review URL: https://codereview.chromium.org/49773003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@234172 0039d316-1c4b-4281-b951-d872f2087c98
Extract XPS code from PrintSystemWin.

BUG=317027

Review URL: https://codereview.chromium.org/61673004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@234174 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 234172
SVN changes up to revision 234174