[gn] Initialize gn for stand-alone v8

BUG=chromium:474921
LOG=n

Review-Url: https://codereview.chromium.org/1936123002
Cr-Commit-Position: refs/heads/master@{#35939}

.gn

+# This file is used by the GN meta build system to find the root of the source
+# tree and to set startup options. For documentation on the values set in this
+# file, run "gn help dotfile" at the command line.
+
+# The location of the build configuration file.
+buildconfig = "//build/config/BUILDCONFIG.gn"
+
+# The secondary source root is a parallel directory tree where
+# GN build files are placed when they can not be placed directly
+# in the source tree, e.g. for third party source trees.
+secondary_source = "//build/secondary/"
+
+# These are the targets to check headers for by default. The files in targets
+# matching these patterns (see "gn help label_pattern" for format) will have
+# their includes checked for proper dependencies when you run either
+# "gn check" or "gn gen --check".
+check_targets = [
+]
+
+# These are the list of GN files that run exec_script. This whitelist exists
+# to force additional review for new uses of exec_script, which is strongly
+# discouraged except for gypi_to_gn calls.
+exec_script_whitelist = [
+  "//build/config/android/BUILD.gn",
+  "//build/config/android/config.gni",
+  "//build/config/android/internal_rules.gni",
+  "//build/config/android/rules.gni",
+  "//build/config/BUILD.gn",
+  "//build/config/compiler/BUILD.gn",
+  "//build/config/gcc/gcc_version.gni",
+  "//build/config/ios/ios_sdk.gni",
+  "//build/config/linux/BUILD.gn",
+  "//build/config/linux/pkg_config.gni",
+  "//build/config/mac/mac_sdk.gni",
+  "//build/config/sysroot.gni",
+  "//build/config/win/visual_studio_version.gni",
+  "//build/toolchain/gcc_toolchain.gni",
+  "//build/toolchain/mac/BUILD.gn",
+  "//build/toolchain/win/BUILD.gn",
+]

build_overrides/v8.gni

+# Copyright 2015 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.
+
+import("//build/config/features.gni")
+import("//build/config/ui.gni")
+
+if (is_android) {
+  import("//build/config/android/config.gni")
+}
+
+v8_use_external_startup_data = false
+v8_optimized_debug = false
+v8_extra_library_files = []
+v8_experimental_extra_library_files = []