Implement IdentityMap<V>, a robust, GC-safe object-identity HashMap.

tools/gyp/v8.gyp

 # 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
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 #     * Redistributions in binary form must reproduce the above
 #       copyright notice, this list of conditions and the following
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@@ skipping 641 matching lines @@
         '../../src/heap-snapshot-generator-inl.h',
         '../../src/heap-snapshot-generator.cc',
         '../../src/heap-snapshot-generator.h',
         '../../src/heap/gc-idle-time-handler.cc',
         '../../src/heap/gc-idle-time-handler.h',
         '../../src/heap/gc-tracer.cc',
         '../../src/heap/gc-tracer.h',
         '../../src/heap/heap-inl.h',
         '../../src/heap/heap.cc',
         '../../src/heap/heap.h',
+        '../../src/heap/identity-map.cc',
+        '../../src/heap/identity-map.h',
         '../../src/heap/incremental-marking-inl.h',
         '../../src/heap/incremental-marking.cc',
         '../../src/heap/incremental-marking.h',
         '../../src/heap/mark-compact-inl.h',
         '../../src/heap/mark-compact.cc',
         '../../src/heap/mark-compact.h',
         '../../src/heap/objects-visiting-inl.h',
         '../../src/heap/objects-visiting.cc',
         '../../src/heap/objects-visiting.h',
         '../../src/heap/spaces-inl.h',
@@ skipping 1172 matching lines @@
         }],
         ['want_separate_host_toolset==1', {
           'toolsets': ['host'],
         }, {
           'toolsets': ['target'],
         }],
       ],
     },
   ],
 }