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

src/api.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 629 matching lines @@
     ASSERT(!isolate->IsInitialized());
     bool result = isolate->heap()->ConfigureHeap(young_space_size / 2,
                                                  old_gen_size,
                                                  max_executable_size);
     if (!result) return false;
   }
   if (constraints->stack_limit() != NULL) {
     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);
   }
   return true;
 }
 
 
 i::Object** V8::GlobalizeReference(i::Isolate* isolate, i::Object** obj) {
   if (IsDeadCheck(isolate, "V8::Persistent::New")) return NULL;
   LOG_API(isolate, "Persistent::New");
@@ skipping 7232 matching lines @@
   Isolate* isolate = reinterpret_cast<Isolate*>(info.GetIsolate());
   Address callback_address =
       reinterpret_cast<Address>(reinterpret_cast<intptr_t>(callback));
   VMState<EXTERNAL> state(isolate);
   ExternalCallbackScope call_scope(isolate, callback_address);
   callback(info);
 }
 
 
 } }  // namespace v8::internal