Enable weak embedded maps in optimized code by default.

src/flag-definitions.h

 // 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 397 matching lines @@
             "print cumulative GC statistics in name=value format on exit")
 DEFINE_bool(trace_gc_verbose, false,
             "print more details following each garbage collection")
 DEFINE_bool(trace_fragmentation, false,
             "report fragmentation for old pointer and data pages")
 DEFINE_bool(trace_external_memory, false,
             "print amount of external allocated memory after each time "
             "it is adjusted.")
 DEFINE_bool(collect_maps, true,
             "garbage collect maps from which no objects can be reached")
-DEFINE_bool(weak_embedded_maps_in_optimized_code, false,
+DEFINE_bool(weak_embedded_maps_in_optimized_code, true,
             "make maps embedded in optimized code weak")
 DEFINE_bool(flush_code, true,
             "flush code that we expect not to use again (during full gc)")
 DEFINE_bool(flush_code_incrementally, true,
             "flush code that we expect not to use again (incrementally)")
 DEFINE_bool(age_code, true,
             "track un-executed functions to age code and flush only "
             "old code")
 DEFINE_bool(incremental_marking, true, "use incremental marking")
 DEFINE_bool(incremental_marking_steps, true, "do incremental marking steps")
@@ skipping 312 matching lines @@
 #undef DEFINE_bool
 #undef DEFINE_int
 #undef DEFINE_string
 #undef DEFINE_implication
 
 #undef FLAG_MODE_DECLARE
 #undef FLAG_MODE_DEFINE
 #undef FLAG_MODE_DEFINE_DEFAULTS
 #undef FLAG_MODE_META
 #undef FLAG_MODE_DEFINE_IMPLICATIONS