[Isolates] Allow running multiple isolates in shell and use this in tests.

src/allocation-inl.h

 // Copyright 2010 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 40 matching lines @@
   Isolate* isolate = Isolate::Current();
   if (allowed_ == DISALLOW) {
     isolate->set_allocation_disallowed(isolate->allocation_disallowed() - 1);
   }
   ASSERT(isolate->allocation_disallowed() >= 0);
 #endif
 }
 
 
 bool NativeAllocationChecker::allocation_allowed() {
+#ifdef DEBUG
   return Isolate::Current()->allocation_disallowed() == 0;
+#else
+  return true;
+#endif  // DEBUG
 }
 
 
 void* PreallocatedStorage::New(size_t size) {
   return Isolate::Current()->PreallocatedStorageNew(size);
 }
 
 
 void PreallocatedStorage::Delete(void* p) {
   return Isolate::Current()->PreallocatedStorageDelete(p);
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_ALLOCATION_INL_H_