[parser] Ship preparser scope analysis under future.

This won't affect the real release but will give more clusterfuzz + test
coverage on V8 side.

BUG=v8:5516

Change-Id: I6ed29b1a1b23b5bf1ce9a9a9dfe741c53312ee54
Reviewed-on: https://chromium-review.googlesource.com/640373Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47664}

src/flag-definitions.h

@@ -267,6 +267,8 @@ DEFINE_BOOL(future, FUTURE_BOOL,
             "Implies all staged features that we want to ship in the "
             "not-too-far future")
 
+DEFINE_IMPLICATION(future, preparser_scope_analysis)
+
 // Flags for experimental implementation features.
 DEFINE_BOOL(allocation_site_pretenuring, true,
             "pretenure with allocation sites")