Add a fake DriveFS launcher client.

Using DriveFS requires building and deploying ChromeOS. Add a client for
the fake DriveFS launcher to allow the use of a real DriveFS from a
ChromeOS chroot to be used with a target_os="chromeos" build of chrome.
This connects to the fake DriveFS launcher using mojo over a unix domain
socket named by a command-line flag, using the launcher to create
DriveFS instances.

Bug: 848126
Change-Id: I22dcca154d41bda196dd7c1782bb503f6bcba5b1
Reviewed-on: https://chromium-review.googlesource.com/1098434
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Sam McNally <sammc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#567513}
bool IsZipArchiverPackerEnabled() {
  return !base::CommandLine::ForCurrentProcess()->HasSwitch(
      kDisableZipArchiverPacker);
}

bool IsZipArchiverPackerEnabled() {
  return !base::CommandLine::ForCurrentProcess()->HasSwitch(
      kDisableZipArchiverPacker);
}
