Add a --read-from-tcp flag to d8, which makes file reads (including
reading files from arguments, and the load and read builtins) read the
file contents off a TCP socket using a simple request/response protocol.

On top of this, add a script for transparently running d8 on an android
device using adb. The script loads d8 onto the device, starts a file
server providing the above protocol, and uses the above flag to run a d8
which loads javascript sources off the computer rather than off the
device.

Change-Id: Icaa0577beb9bcd4f93476faa3ad8fb8b0a165e6e
Reviewed-on: https://chromium-review.googlesource.com/623790
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47511}