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

src/flag-definitions.h

Index: src/flag-definitions.h
diff --git a/src/flag-definitions.h b/src/flag-definitions.h
index 7548c01643615a0a9b293389dc4c6206120d91f2..07329c0a12f507d36b8f7d096bc0b2d363383ccb 100644
--- a/src/flag-definitions.h
+++ b/src/flag-definitions.h
@@ -148,6 +148,8 @@ public:
 #endif
 
 #define DEFINE_bool(nam, def, cmt)   FLAG(BOOL, bool, nam, def, cmt)
+#define DEFINE_maybe_bool(nam, cmt)  FLAG(MAYBE_BOOL, Maybe<bool>, nam,  \
+                                          Maybe<bool>(), cmt)
 #define DEFINE_int(nam, def, cmt)    FLAG(INT, int, nam, def, cmt)
 #define DEFINE_float(nam, def, cmt)  FLAG(FLOAT, double, nam, def, cmt)
 #define DEFINE_string(nam, def, cmt) FLAG(STRING, const char*, nam, def, cmt)
@@ -601,6 +603,9 @@ DEFINE_int(hash_seed,
            0,
            "Fixed seed to use to hash property keys (0 means random)"
            "(with snapshots this option cannot override the baked-in seed)")
+DEFINE_maybe_bool(force_memory_constrained,
+           "force (if true) or prevent (if false) the runtime from treating "
+           "the device as being memory constrained.")
 
 // v8.cc
 DEFINE_bool(preemption, false,
@@ -835,6 +840,7 @@ DEFINE_implication(print_all_code, trace_codegen)
 #undef FLAG_ALIAS
 
 #undef DEFINE_bool
+#undef DEFINE_maybe_bool
 #undef DEFINE_int
 #undef DEFINE_string
 #undef DEFINE_float