Build update_engine_sideload.
Add a new "sideload" executable target that applies an update payload
directly using the UpdateAttempterAndroid.
This initial CL buils a dynamically linked program that's targeted to
run in the system image for now, but will later be transformed into a
static binary to run from the recovery environment.
Bug: 27178350
TEST=Applied a payload directly on a device using:
`update_engine_sideload --payload=file://foo/bar ...`
(cherry picked from commit 03a4de7dc77b058987fc0670f4f67ba10ff31bc8)
Change-Id: Idbde52fff9ace53c03f34103664f51b9db45027d
8 files changed
