Allow embedder to set promise internal field count

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index 14c7a696e651f583b47d88d243b45a337735270d..6ca4cb53074a3224a5b9c35bdeeab9855ac93175 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -45,6 +45,9 @@ declare_args() {
   # Sets -dENABLE_DISASSEMBLER.
   v8_enable_disassembler = ""
 
+  # Sets the number of internal fields on promise objects.
+  v8_promise_internal_field_count = ""

[jochen (gone - plz use gerrit), 2017/05/23 11:19:49]

that should be a number, no?

[mattloring, 2017/05/23 16:54:42]

Done.

+
   # Sets -dENABLE_GDB_JIT_INTERFACE.
   v8_enable_gdbjit = ""
 
@@ -206,6 +209,9 @@ config("features") {
   if (v8_enable_disassembler) {
     defines += [ "ENABLE_DISASSEMBLER" ]
   }
+  if (v8_promise_internal_field_count) {
+    defines += [ "V8_PROMISE_INTERNAL_FIELD_COUNT" ]

[jochen (gone - plz use gerrit), 2017/05/23 11:19:49]

and that should be
V8_PROMISE_INTERNAL_FIELD_COUNT=${v8_promise_internal_field_count}

[mattloring, 2017/05/23 16:54:43]

Done.

+  }
   if (v8_enable_future) {
     defines += [ "V8_ENABLE_FUTURE" ]
   }