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

BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/android/config.gni")
 import("//build/config/arm.gni")
 import("//build/config/mips.gni")
 
 # Because standalone V8 builds are not supported, assume this is part of a
 # Chromium build.
@@ skipping 751 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.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",
     "src/heap/spaces.cc",
@@ skipping 822 matching lines @@
       sources += [
         "src/d8-debug.cc",
         "$target_gen_dir/d8-js.cc",
       ]
     }
     if (v8_enable_i18n_support) {
       deps += [ "//third_party/icu" ]
     }
   }
 }