Enable SharedArrayBuffer by default in standalone v8.

BUG=chromium:709179
R=binji@chromium.org,hablich@chromium.org

Change-Id: I2efb3becc1ca9fef84008c82cd882ef11e2aa3f2
Reviewed-on: https://chromium-review.googlesource.com/589768
Commit-Queue: Brad Nelson <bradnelson@chromium.org>
Reviewed-by: Ben Smith <binji@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46986}

src/flag-definitions.h

@@ -192,7 +192,6 @@ DEFINE_IMPLICATION(es_staging, harmony)
 #define HARMONY_INPROGRESS_BASE(V)                                    \
   V(harmony_array_prototype_values, "harmony Array.prototype.values") \
   V(harmony_function_sent, "harmony function.sent")                   \
-  V(harmony_sharedarraybuffer, "harmony sharedarraybuffer")           \
   V(harmony_do_expressions, "harmony do-expressions")                 \
   V(harmony_class_fields, "harmony public fields in class literals")  \
   V(harmony_async_iteration, "harmony async iteration")               \
@@ -228,6 +227,7 @@ DEFINE_IMPLICATION(es_staging, harmony)
   V(harmony_restrictive_generators,                                      \
     "harmony restrictions on generator declarations")                    \
   V(harmony_object_rest_spread, "harmony object rest spread properties") \
+  V(harmony_sharedarraybuffer, "harmony sharedarraybuffer")              \
   V(harmony_regexp_dotall, "harmony regexp dotAll flag")
 
 // Once a shipping feature has proved stable in the wild, it will be dropped