GitLab

This is preparation to split ArcSession running part
from ArcbridgeService.
- Remove friend test declaration, and use public interface only.
- Rework ArcBridgeTest so that we can almost simply rename
  the ArcBridgeServiceImpl.
- Use EXPECT rather than ASSERT.

BUG=657687
BUG=b/31079732
TEST=Ran bots.

Review-Url: https://codereview.chromium.org/2581533004
Cr-Commit-Position: refs/heads/master@{#439373}