Manually skipping merge commit '167c3f6' into nyc-mr1-dev-plus-aosp
because it was cherry picked from aosp (stephenli@ on advice of deymo@)
* commit '167c3f6':
Setup a temporary directory for update_engine_sideload.
DO NOT MERGE: Make update_engine compile in the branch.
New setting to mark postinstall as optional.
Report the progress of the update when sideloading.
Compile update_engine_sideload as a static recovery program.
Remove libcurl support from update_engine_sideload.
Build update_engine_sideload.
Implement a memory-based Prefs class.