[compiler] array index masking on --future

Bug: 
Change-Id: I3185f0e88f0eef3d5a9b58a28cb6d103851da473
Reviewed-on: https://chromium-review.googlesource.com/839763
Commit-Queue: Michael Stanton <mvstanton@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50269}

src/flag-definitions.h

@@ -465,6 +465,7 @@ DEFINE_BOOL(turbo_rewrite_far_jumps, true,
             "rewrite far to near jumps (ia32,x64)")
 DEFINE_BOOL(extra_masking, false, "Extra mask for memory accesses")
 DEFINE_BOOL(mask_array_index, false, "Mask array index with bound")
+DEFINE_IMPLICATION(future, extra_masking)
 DEFINE_IMPLICATION(extra_masking, mask_array_index)
 
 // Flags to help platform porters