... but be less pessimistic about context allocation (see below).

We might have just (pessimistically) context-allocated a variable based
on references coming from an inner function, but after that we still
need to set maybe_assigned (pessimistically).

This makes test-parsing/InnerAssignment pass with
FLAG_lazy_inner_functions.

This was undetected until now because we didn't have lazy parsing enabled
for small scripts.

Less pessimistic approach: now that inner functions laziness decisions
are stable (if we have once compiled a piece of code with lazy inner
functions, we never compile the same code with eager inner functions),
we don't need to be as pessimistic with context allocation as before.

BUG=v8:5501

Review-Url: https://codereview.chromium.org/2521513004
Cr-Commit-Position: refs/heads/master@{#41183}