smbprovider: Generalize operation errors

This change adds more generic Start/Continue operation errors and method
constants for Start/ContinueReadDirectory.

BUG=chromium:757625
TEST=emerges
Change-Id: Ic73faa628e3e825190e4d46ddaa3d1f671054edd
Reviewed-on: https://chromium-review.googlesource.com/1226156
Commit-Ready: Bailey Berro <baileyberro@chromium.org>
Tested-by: Bailey Berro <baileyberro@chromium.org>
Reviewed-by: Zentaro Kavanagh <zentaro@chromium.org>
2 files changed