GitLab

It is slightly weird for ArcServiceManager to handle (only) one of the
ArcService instances it has in a special way with inheritance, and this
CL fixes that. ArcServiceManager looks more neutral now and no longer
has to #include arc_intent_helper_observer.h on the header side. This
removes all virtual member functions from ArcServiceManager too.

Instead, do the same thing with a pair of member variable and its getter
function, which is more consistent with the existing ArcServiceManager
code. All the implementation details go to the .cc side.

This is a follow-up CL for
https://codereview.chromium.org/2487623002/.

BUG=672840
TEST=try

Review-Url: https://codereview.chromium.org/2538263005
Cr-Commit-Position: refs/heads/master@{#438718}