Refactor ArcSessionRunner part 1.

This CL renames ArcBridgeServiceImpl to ArcSessionRunner,
and had  as a preparation to get rid of inheritance.
Along with the change, FakeArcBridgeService is removed
and replaced by ArcSessionRunner + FakeArcSession factory.

[email protected]
BUG=657687
BUG=b/31079732
TEST=Ran bots.

Review-Url: https://codereview.chromium.org/2574013003
Cr-Commit-Position: refs/heads/master@{#440019}
22 files changed