[es6] Stage tail call elimination.

src/flag-definitions.h

Index: src/flag-definitions.h
diff --git a/src/flag-definitions.h b/src/flag-definitions.h
index 6419726f3fa6b348257c6e35b8aaf7b30e2c7904..f27c69f0ab18802b08d8e0cb0c2e1cc6a670aea5 100644
--- a/src/flag-definitions.h
+++ b/src/flag-definitions.h
@@ -195,7 +195,6 @@ DEFINE_NEG_IMPLICATION(harmony, promise_extra)
 // Activate on ClusterFuzz.
 DEFINE_IMPLICATION(es_staging, harmony_regexp_lookbehind)
 DEFINE_IMPLICATION(es_staging, move_object_start)
-DEFINE_IMPLICATION(es_staging, harmony_tailcalls)
 
 // Features that are still work in progress (behind individual flags).
 #define HARMONY_INPROGRESS(V)                                           \
@@ -204,13 +203,13 @@ DEFINE_IMPLICATION(es_staging, harmony_tailcalls)
   V(harmony_sharedarraybuffer, "harmony sharedarraybuffer")             \
   V(harmony_simd, "harmony simd")                                       \
   V(harmony_do_expressions, "harmony do-expressions")                   \
-  V(harmony_tailcalls, "harmony tail calls")                            \
   V(harmony_regexp_property, "harmony unicode regexp property classes")
 
 // Features that are complete (but still behind --harmony/es-staging flag).
 #define HARMONY_STAGED(V)                                                    \
   V(harmony_regexp_lookbehind, "harmony regexp lookbehind")                  \
   V(harmony_instanceof, "harmony instanceof support")                        \
+  V(harmony_tailcalls, "harmony tail calls")                                 \
   V(harmony_object_values_entries, "harmony Object.values / Object.entries") \
   V(harmony_object_own_property_descriptors,                                 \
     "harmony Object.getOwnPropertyDescriptors()")                            \