[es6] Stage array spread

BUG=v8:3018
LOG=N

Review URL: https://codereview.chromium.org/1165653003

Cr-Commit-Position: refs/heads/master@{#28744}

src/flag-definitions.h

@@ -193,14 +193,14 @@ DEFINE_IMPLICATION(es_staging, harmony)
   V(harmony_unicode_regexps, "harmony unicode regexps")         \
   V(harmony_reflect, "harmony Reflect API")                     \
   V(harmony_destructuring, "harmony destructuring")             \
-  V(harmony_spread_arrays, "harmony spread in array literals")  \
   V(harmony_sharedarraybuffer, "harmony sharedarraybuffer")
 
 // Features that are complete (but still behind --harmony/es-staging flag).
 #define HARMONY_STAGED(V)                               \
   V(harmony_rest_parameters, "harmony rest parameters") \
   V(harmony_spreadcalls, "harmony spread-calls")        \
-  V(harmony_object, "harmony Object methods")
+  V(harmony_object, "harmony Object methods")           \
+  V(harmony_spread_arrays, "harmony spread in array literals")
 
 // Features that are shipping (turned on by default, but internal flag remains).
 #define HARMONY_SHIPPING(V)                                                \