Moving some CPL logic to CPLH.

In preparation of the move of some of the child process launcher logic to
base, moved the code responsible for building the parameters passed to
the service from ChildProcessLauncher to ChildProcessLauncherHelper.
The ChildSpawnData class now contains both bundles used when starting the
service, and it's the responsibility of the ChildProcessLauncherHelper to
include the command line and file descriptors in the bundles.

BUG=702316

Review-Url: https://codereview.chromium.org/2882823002
Cr-Commit-Position: refs/heads/master@{#472494}
10 files changed