Add gn flag for enabling javascript promise hooks

Change-Id: Iae17977cec9520cf0194b5686ec31f0501f866f1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2839556
Auto-Submit: Jochen Eisinger <jochen@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74063}

BUILD.gn

@@ -309,6 +309,9 @@ declare_args() {
 
   # Enable map packing & unpacking (sets -dV8_MAP_PACKING).
   v8_enable_map_packing = false
+
+  # Allow for JS promise hooks (instead of just C++).
+  v8_allow_javascript_in_promise_hooks = false
 }
 
 # Derived defaults.
@@ -837,6 +840,9 @@ config("features") {
   if (v8_dict_property_const_tracking) {
     defines += [ "V8_DICT_PROPERTY_CONST_TRACKING" ]
   }
+  if (v8_allow_javascript_in_promise_hooks) {
+    defines += [ "V8_ALLOW_JAVASCRIPT_IN_PROMISE_HOOKS" ]
+  }
 }
 
 config("toolchain") {