Add flags to force or prevent setting of isolate.is_memory_constrained.

src/api.cc

Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index d1f6b78cc0c1d06b0d252071d8bf6c0a2573d5ee..817ae1c5e4c6eed33cc6ec82ac225893e55e5714 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -647,7 +647,8 @@ bool SetResourceConstraints(ResourceConstraints* constraints) {
     uintptr_t limit = reinterpret_cast<uintptr_t>(constraints->stack_limit());
     isolate->stack_guard()->SetStackLimit(limit);
   }
-  if (constraints->is_memory_constrained().has_value) {
+  if (constraints->is_memory_constrained().has_value &&
+      !i::FLAG_force_memory_constrained.has_value) {
     isolate->set_is_memory_constrained(
         constraints->is_memory_constrained().value);
   }