Remove unused maps during marking garbage collections.

src/flag-definitions.h

 // Copyright 2008 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 116 matching lines @@
 DEFINE_int(max_stack_trace_source_length, 300,
            "maximum length of function source code printed in a stack trace.")
 
 // heap.cc
 DEFINE_int(new_space_size, 0, "size of (each semispace in) the new generation")
 DEFINE_int(old_space_size, 0, "size of the old generation")
 DEFINE_bool(gc_global, false, "always perform global GCs")
 DEFINE_int(gc_interval, -1, "garbage collect after <n> allocations")
 DEFINE_bool(trace_gc, false,
             "print one trace line following each garbage collection")
+DEFINE_bool(collect_maps, true,
+            "garbage collect maps from which no objects can be reached")
 
 // ic.cc
 DEFINE_bool(use_ic, true, "use inline caching")
 
 // macro-assembler-ia32.cc
 DEFINE_bool(native_code_counters, false,
             "generate extra code for manipulating stats counters")
 
 // mark-compact.cc
 DEFINE_bool(always_compact, false, "Perform compaction on every full GC")
@@ skipping 168 matching lines @@
 #undef FLAG
 
 #undef DEFINE_bool
 #undef DEFINE_int
 #undef DEFINE_string
 
 #undef FLAG_MODE_DECLARE
 #undef FLAG_MODE_DEFINE
 #undef FLAG_MODE_DEFINE_DEFAULTS
 #undef FLAG_MODE_META