Add safe numerics classes, imported from Chromium

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.
 
 # TODO(jochen): These will need to be user-settable to support standalone V8
 # builds.
 v8_compress_startup_data = "off"
 v8_deprecation_warnings = false
 v8_enable_disassembler = false
 v8_enable_gdbjit = false
@@ skipping 958 matching lines @@
     "src/base/atomicops_internals_mips_gcc.h",
     "src/base/atomicops_internals_tsan.h",
     "src/base/atomicops_internals_x86_gcc.cc",
     "src/base/atomicops_internals_x86_gcc.h",
     "src/base/atomicops_internals_x86_msvc.h",
     "src/base/build_config.h",
     "src/base/lazy-instance.h",
     "src/base/macros.h",
     "src/base/once.cc",
     "src/base/once.h",
+    "src/base/safe_conversions.h",
+    "src/base/safe_conversions_impl.h",
+    "src/base/safe_math.h",
+    "src/base/safe_math_impl.h",
     "src/base/win32-headers.h",
   ]
 
   configs -= [ "//build/config/compiler:chromium_code" ]
   configs += [ "//build/config/compiler:no_chromium_code" ]
   configs += [ ":internal_config", ":features", ":toolchain" ]
 }
 
 ###############################################################################
 # Executables
@@ skipping 68 matching lines @@
     deps = [
       ":v8_base",
       ":v8_nosnapshot",
     ]
   }
 
   direct_dependent_configs = [ ":external_config" ]
 }
 
 }