Adds a scavenge GC pass to collect unmodified references

src/flag-definitions.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This file defines all of the flags.  It is separated into different section,
 // for Debug, Release, Logging and Profiling, etc.  To add a new flag, find the
 // correct section, and use one of the DEFINE_ macros, without a trailing ';'.
 //
 // This include does not have a guard, because it is a template-style include,
 // which can be included multiple times in different modes.  It expects to have
@@ skipping 663 matching lines @@
 DEFINE_BOOL(track_detached_contexts, true,
             "track native contexts that are expected to be garbage collected")
 DEFINE_BOOL(trace_detached_contexts, false,
             "trace native contexts that are expected to be garbage collected")
 DEFINE_IMPLICATION(trace_detached_contexts, track_detached_contexts)
 #ifdef VERIFY_HEAP
 DEFINE_BOOL(verify_heap, false, "verify heap pointers before and after GC")
 #endif
 DEFINE_BOOL(move_object_start, false, "enable moving of object starts")
 DEFINE_BOOL(memory_reducer, true, "use memory reducer")
+DEFINE_BOOL(scavenge_reclaim_unmodified_objects, false,
+            "remove unmodified and unreferenced objects")
 
 // counters.cc
 DEFINE_INT(histogram_interval, 600000,
            "time interval in ms for aggregating memory histograms")
 
 
 // heap-snapshot-generator.cc
 DEFINE_BOOL(heap_profiler_trace_objects, false,
             "Dump heap object allocations/movements/size_updates")
 
@@ skipping 411 matching lines @@
 #undef DEFINE_ALIAS_FLOAT
 #undef DEFINE_ALIAS_ARGS
 
 #undef FLAG_MODE_DECLARE
 #undef FLAG_MODE_DEFINE
 #undef FLAG_MODE_DEFINE_DEFAULTS
 #undef FLAG_MODE_META
 #undef FLAG_MODE_DEFINE_IMPLICATIONS
 
 #undef COMMA