Clean-up of ChildProcessLauncherHelper.stop()

ChildProcessLauncherHelper calls stop method when a child process dies,
which ends up stopping the connection when the connection is already
stopped. Cleaning it up by abstracting the behavior on disconnection
to an onChildProcessStopped method.
Also improving tests to ensure this onChildProcessStopped is called.

Bug: 702316
Change-Id: I348d347ea8b6903886565d4a3c7ede7d30def6f5
Reviewed-on: https://chromium-review.googlesource.com/546698
Commit-Queue: Jay Civelli <jcivelli@chromium.org>
Reviewed-by: Bo Liu <boliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#482048}
2 files changed