Move //build/module_args/v8.gni to //build_overrides.

The original intent of the build/module_args directory was to
provide a place where different repos could customize settings
as needed depending on their dependencies and needs.

However, given that you can't really yet embed GN by just
deps-ing in //build/config and //build/toolchain, you end up
needing to deps-in all of build, and so there was no good way to
have different settings per-repo in //build/module_args.

This CL changes the approach such that we will have an additional
top-level directory called //build_overrides, which is therefore
separate from //build and can be properly customized.

It is unfortunate that we need to use two top-level directories
for GN, but we don't have a good alternative at this time. Once
we can remove the GYP build and further clean up the structure
and dependencies of //build we will hopefully be able to do better.

R=brettw@chromium.org
BUG=541791

Review URL: https://codereview.chromium.org/1397493004

Cr-Original-Commit-Position: refs/heads/master@{#353690}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: d4da5ab4987c2c22d96dcf8c4b3ac2449aa16c0f

config/BUILD.gn

@@ -8,7 +8,7 @@ import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/config/ui.gni")
-import("//build/module_args/v8.gni")
+import("//build_overrides/v8.gni")
 import("//build/toolchain/goma.gni")
 
 declare_args() {

module_args/v8.gni

@@ -2,19 +2,7 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-if (is_android) {
-  import("//build/config/android/config.gni")
-}
+# TODO(dpranke): Remove this file altogether once v8 has been updated
+# to import //build_overrides/v8.gni instead.
 
-# TODO(sky): nuke this. Temporary while sorting out http://crbug.com/465456.
-enable_correct_v8_arch = false
-
-v8_use_external_startup_data = !(is_chromeos || is_win || is_ios)
-
-# V8 extras
-# Adding V8 extras files requires API owners review
-# Be sure to synchronize with build/common.gypi
-
-v8_extra_library_files = []
-v8_experimental_extra_library_files =
-    [ "../third_party/WebKit/Source/core/streams/ByteLengthQueuingStrategy.js" ]
+import("//build_overrides/v8.gni")