The parser eagerly rewrites destructuring assignments occuring
in formal parameter initializers, because not doing so would
cause the BindingPattern rewriting to be confused and do the
wrong thing.

This change prevents this rewriting from descending into the
bodies of lazily parsed functions.

In general, it's a mistake to descend into the bodies of function
literals anyways, since they are rewritten separately on their
own time, so there is no distinction made between lazily
"throw away" eagerly parsed functions in the temporary parser
arena, or "real" eagerly parsed functions that will be compiled.

BUG=chromium:594084, v8:811
LOG=N
R=adamk@chromium.org, littledan@chromium.org

Review URL: https://codereview.chromium.org/1864553002

Cr-Commit-Position: refs/heads/master@{#35277}