[es6] Stage unicode escapes in strings, var names etc.

R=rossberg@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1071533002

Cr-Commit-Position: refs/heads/master@{#27660}

src/flag-definitions.h

@@ -190,7 +190,6 @@ DEFINE_IMPLICATION(es_staging, harmony)
   V(harmony_arrow_functions, "harmony arrow functions")         \
   V(harmony_proxies, "harmony proxies")                         \
   V(harmony_sloppy, "harmony features in sloppy mode")          \
-  V(harmony_unicode, "harmony unicode escapes")                 \
   V(harmony_unicode_regexps, "harmony unicode regexps")         \
   V(harmony_rest_parameters, "harmony rest parameters")         \
   V(harmony_reflect, "harmony Reflect API")
@@ -198,7 +197,8 @@ DEFINE_IMPLICATION(es_staging, harmony)
 // Features that are complete (but still behind --harmony/es-staging flag).
 #define HARMONY_STAGED(V)                                               \
   V(harmony_computed_property_names, "harmony computed property names") \
-  V(harmony_tostring, "harmony toString")
+  V(harmony_tostring, "harmony toString")                               \
+  V(harmony_unicode, "harmony unicode escapes")
 
 // Features that are shipping (turned on by default, but internal flag remains).
 #define HARMONY_SHIPPING(V)                                                \