In order to allow parallel compilation of eager inner functions, we need to
seperate the zone used for parsing (which will be shared between all the
parallel compile jobs) and the zone used for compilation. This CL changes
CompilationInfo to require a zone (which can be different from the zone in
ParseInfo). We then seal the ParseInfo zone after parsing and analysis is done
to prevent any further allocation in that zone, so that it can be shared
(read-only) with the parallel compile jobs.

BUG=v8:5203

Review-Url: https://codereview.chromium.org/2645403002
Cr-Commit-Position: refs/heads/master@{#43089}