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-Commit-Position: refs/heads/master@{#353690}

2 files changed, 40 insertions, 0 deletions

diff --git a/build_overrides/README.md b/build_overrides/README.md
new file mode 100644
index 0000000..d26312c
--- /dev/null
+++ b/build_overrides/README.md
@@ -0,0 +1,20 @@
+# Build overrides in GN
+
+This directory is used to allow different products to customize settings
+for repos that are DEPS'ed in or shared.
+
+For example: V8 could be built on its own (in a "standalone" configuration),
+and it could be built as part of Chromium. V8 might define a top-level
+target, //v8:d8 (a simple executable), that should only be built in the
+standalone configuration. To figure out whether or not it should be
+in a standalone configuration, v8 can create a file, build_overrides/v8.gni,
+that contains a variable, `build_standalone_d8 = true`.
+and import it (as import("//build_overrides/v8.gni") from its top-level
+BUILD.gn file.
+
+Chromium, on the other hand, might not need to build d8, and so it would
+create its own build_overrides/v8.gni file, and in it set 
+`build_standalone_d8 = false`. 
+
+The two files should define the same set of variables, but the values can
+vary as appropriate to the needs of the two different builds.
diff --git a/build_overrides/v8.gni b/build_overrides/v8.gni
new file mode 100644
index 0000000..4fc5f98
--- /dev/null
+++ b/build_overrides/v8.gni
@@ -0,0 +1,20 @@
+# Copyright 2015 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.
+
+if (is_android) {
+  import("//build/config/android/config.gni")
+}
+
+# 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" ]