Fix GN arm64 build, add msan support in GN.

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.
 import("//build/module_args/v8.gni")
 
 # TODO(jochen): These will need to be user-settable to support standalone V8
 # builds.
 v8_deprecation_warnings = false
 v8_enable_disassembler = false
 v8_enable_gdbjit = false
 v8_enable_handle_zapping = true
 v8_enable_i18n_support = true
 v8_enable_verify_heap = false
 v8_interpreted_regexp = false
 v8_object_print = false
 v8_postmortem_support = false
 v8_use_snapshot = true
-v8_target_arch = target_cpu
 v8_random_seed = "314159265"
 v8_toolset_for_d8 = "host"
 
+if (is_msan) {

[adamk, 2015/09/01 21:48:32]

Why is this arm64 only? My gyp-fu is weak, but I don't see a similar stanza in
the gyp files.

I'd appreciate a comment here, otherwise this looks like pure magic.

+  v8_target_arch = "arm64"
+} else {
+  v8_target_arch = target_cpu
+}
+
 # The snapshot needs to be compiled for the host, but compiled with
 # a toolchain that matches the bit-width of the target.
 #
 # TODO(GYP): For now we only support 32-bit little-endian target builds from an
 # x64 Linux host. Eventually we need to support all of the host/target
 # configurations v8 runs on.
 if (host_cpu == "x64" && host_os == "linux") {
   if (target_cpu == "arm" || target_cpu == "mipsel" || target_cpu == "x86") {
     snapshot_toolchain = "//build/toolchain/linux:clang_x86"
   } else if (target_cpu == "x64") {
@@ skipping 1334 matching lines @@
       "src/arm64/builtins-arm64.cc",
       "src/arm64/codegen-arm64.cc",
       "src/arm64/codegen-arm64.h",
       "src/arm64/code-stubs-arm64.cc",
       "src/arm64/code-stubs-arm64.h",
       "src/arm64/constants-arm64.h",
       "src/arm64/cpu-arm64.cc",
       "src/arm64/decoder-arm64.cc",
       "src/arm64/decoder-arm64.h",
       "src/arm64/decoder-arm64-inl.h",
+      "src/arm64/delayed-masm-arm64.cc",
+      "src/arm64/delayed-masm-arm64.h",
+      "src/arm64/delayed-masm-arm64-inl.h",
       "src/arm64/deoptimizer-arm64.cc",
       "src/arm64/disasm-arm64.cc",
       "src/arm64/disasm-arm64.h",
       "src/arm64/frames-arm64.cc",
       "src/arm64/frames-arm64.h",
       "src/arm64/instructions-arm64.cc",
       "src/arm64/instructions-arm64.h",
       "src/arm64/instrument-arm64.cc",
       "src/arm64/instrument-arm64.h",
       "src/arm64/interface-descriptors-arm64.cc",
@@ skipping 430 matching lines @@
     if (!is_component_build) {
       sources += [
         "$target_gen_dir/d8-js.cc",
       ]
     }
     if (v8_enable_i18n_support) {
       deps += [ "//third_party/icu" ]
     }
   }
 }