[es6] implement spread calls

src/flag-definitions.h

Index: src/flag-definitions.h
diff --git a/src/flag-definitions.h b/src/flag-definitions.h
index d9169f62bed27784f8aac6fd196f67198b1cc237..f94f87867ee33418011b7102acaed78dbaeebc96 100644
--- a/src/flag-definitions.h
+++ b/src/flag-definitions.h
@@ -181,6 +181,7 @@ DEFINE_BOOL(harmony_shipping, true, "enable all shipped harmony fetaures")
 DEFINE_IMPLICATION(harmony, es_staging)
 DEFINE_IMPLICATION(es_staging, harmony)
 
+
 // Features that are still work in progress (behind individual flags).
 #define HARMONY_INPROGRESS(V)                                   \
   V(harmony_modules, "harmony modules")                         \
@@ -193,7 +194,8 @@ DEFINE_IMPLICATION(es_staging, harmony)
   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")
+  V(harmony_reflect, "harmony Reflect API")                     \
+  V(harmony_spreadcalls, "harmony spread-calls")
 
 // Features that are complete (but still behind --harmony/es-staging flag).
 #define HARMONY_STAGED(V)                                               \
@@ -234,7 +236,6 @@ HARMONY_SHIPPING(FLAG_SHIPPING_FEATURES)
 DEFINE_IMPLICATION(harmony_classes, harmony_object_literals)
 DEFINE_IMPLICATION(harmony_unicode_regexps, harmony_unicode)
 
-
 // Flags for experimental implementation features.
 DEFINE_BOOL(compiled_keyed_generic_loads, false,
             "use optimizing compiler to generate keyed generic load stubs")