To avoid a dependency on the heap during parsing, we only create a scope chain
without linking to the associated ScopeInfo objects before parsing. This is
enough to avoid special cases during parsing of arrow functions / eval.

Looking at the outer scope's variables during parsing was only needed for hosting
sloppy block functions inside eval. To be able to do this now, we hoist for the
outer-most eval scope after parsing, in DeclarationScope::Analyze.

DeclarationScope::Analyze is also where we replace the outer scope chain with the
fully deserialized version, so variables can be resolved.

Also, this unifies background and foreground thread parsing, as we don't have to
worry about ScopeInfos getting accessed before we're back on the main thread.

BUG=v8:5215
R=verwaest@chromium.org,marja@chromium.org,adamk@chromium.org

Review-Url: https://codereview.chromium.org/2306413002
Cr-Commit-Position: refs/heads/master@{#39452}