[harmony] unstage regexp lookbehind assertions.

R=hablich@chromium.org
BUG=v8:4545
LOG=Y

Review URL: https://codereview.chromium.org/1524233003

Cr-Commit-Position: refs/heads/master@{#32889}

src/flag-definitions.h

@@ -197,6 +197,7 @@ DEFINE_NEG_IMPLICATION(harmony, promise_extra)
 DEFINE_IMPLICATION(es_staging, harmony_destructuring_assignment)
 DEFINE_IMPLICATION(es_staging, harmony_proxies)
 DEFINE_IMPLICATION(es_staging, harmony_reflect)
+DEFINE_IMPLICATION(es_staging, harmony_regexp_lookbehind)
 
 // Features that are still work in progress (behind individual flags).
 #define HARMONY_INPROGRESS(V)                                             \
@@ -210,13 +211,13 @@ DEFINE_IMPLICATION(es_staging, harmony_reflect)
   V(harmony_simd, "harmony simd")                                         \
   V(harmony_do_expressions, "harmony do-expressions")                     \
   V(harmony_regexp_subclass, "harmony regexp subclassing")                \
-  V(harmony_destructuring_assignment, "harmony destructuring assignment")
+  V(harmony_destructuring_assignment, "harmony destructuring assignment") \
+  V(harmony_regexp_lookbehind, "harmony regexp lookbehind")
 
 // Features that are complete (but still behind --harmony/es-staging flag).
 #define HARMONY_STAGED(V)                              \
   V(harmony_sloppy, "harmony features in sloppy mode") \
-  V(harmony_sloppy_let, "harmony let in sloppy mode")         \
-  V(harmony_regexp_lookbehind, "harmony regexp lookbehind")
+  V(harmony_sloppy_let, "harmony let in sloppy mode")
 
 // Features that are shipping (turned on by default, but internal flag remains).
 #define HARMONY_SHIPPING(V)                                   \