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 cc153af2542dfca612c4e12c579318931190acbd..95fb1f1d4e42be5708855c4758d8554b164f8f5b 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)
@@ -600,6 +602,9 @@ 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,
@@ -610,6 +615,7 @@ DEFINE_bool(regexp_optimization, true, "generate optimized regexp code")
 
 // Testing flags test/cctest/test-{flags,api,serialization}.cc
 DEFINE_bool(testing_bool_flag, true, "testing_bool_flag")
+DEFINE_maybe_bool(testing_maybe_bool_flag, "testing_maybe_bool_flag")
 DEFINE_int(testing_int_flag, 13, "testing_int_flag")
 DEFINE_float(testing_float_flag, 2.5, "float-flag")
 DEFINE_string(testing_string_flag, "Hello, world!", "string-flag")
@@ -834,6 +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