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}

13 files changed, 56 insertions, 34 deletions

diff --git a/BUILD.gn b/BUILD.gn
index f7ca039..e1e2328 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -12,7 +12,7 @@ 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("//media/media_options.gni")
 
 if (is_android) {
diff --git a/build/config/BUILD.gn b/build/config/BUILD.gn
index 4af7389..97d7d04 100644
--- a/build/config/BUILD.gn
+++ b/build/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() {
diff --git a/build/module_args/v8.gni b/build/module_args/v8.gni
index f18bfaf..e1e5fae 100644
--- a/build/module_args/v8.gni
+++ b/build/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")
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" ]
diff --git a/chrome/android/BUILD.gn b/chrome/android/BUILD.gn
index f4263d3..5adb30c 100644
--- a/chrome/android/BUILD.gn
+++ b/chrome/android/BUILD.gn
@@ -4,7 +4,7 @@
 
 import("//build/config/android/config.gni")
 import("//build/config/android/rules.gni")
-import("//build/module_args/v8.gni")
+import("//build_overrides/v8.gni")
 import("//chrome/version.gni")
 import("//testing/test.gni")
 import("//third_party/icu/config.gni")
diff --git a/chrome/installer/mini_installer/BUILD.gn b/chrome/installer/mini_installer/BUILD.gn
index 100f25f..1e20d80 100644
--- a/chrome/installer/mini_installer/BUILD.gn
+++ b/chrome/installer/mini_installer/BUILD.gn
@@ -4,7 +4,7 @@
 
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
-import("//build/module_args/v8.gni")
+import("//build_overrides/v8.gni")
 import("//chrome/version.gni")
 import("//third_party/icu/config.gni")
 
diff --git a/chrome/test/base/js2gtest.gni b/chrome/test/base/js2gtest.gni
index f4b6c76..a995869 100644
--- a/chrome/test/base/js2gtest.gni
+++ b/chrome/test/base/js2gtest.gni
@@ -2,7 +2,7 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import("//build/module_args/v8.gni")
+import("//build_overrides/v8.gni")
 import("//v8/snapshot_toolchain.gni")
 
 # Variables:
diff --git a/components/html_viewer/BUILD.gn b/components/html_viewer/BUILD.gn
index f9a6217..47863ce 100644
--- a/components/html_viewer/BUILD.gn
+++ b/components/html_viewer/BUILD.gn
@@ -2,7 +2,7 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import("//build/module_args/v8.gni")
+import("//build_overrides/v8.gni")
 import("//mojo/public/mojo_application.gni")
 import("//testing/test.gni")
 import("//tools/grit/grit_rule.gni")
@@ -357,9 +357,7 @@ mojo_native_application("apptests") {
     "//third_party/mojo/src/mojo/public/c/system:for_shared_library",
   ]
 
-  data_deps = [
-    ":html_viewer",
-  ]
+  data_deps = [ ":html_viewer" ]
 
   if (is_linux && !is_android) {
     data_deps += [ "//components/font_service" ]
diff --git a/content/shell/android/BUILD.gn b/content/shell/android/BUILD.gn
index d0f3701..6aa4123 100644
--- a/content/shell/android/BUILD.gn
+++ b/content/shell/android/BUILD.gn
@@ -4,7 +4,7 @@
 
 import("//build/config/android/config.gni")
 import("//build/config/android/rules.gni")
-import("//build/module_args/v8.gni")
+import("//build_overrides/v8.gni")
 import("//third_party/icu/config.gni")
 
 generate_jni("content_shell_jni_headers") {
@@ -159,9 +159,7 @@ instrumentation_test_apk("content_shell_test_apk") {
     "//base:base_javatests",
     "//net/android:net_javatests",
   ]
-  data_deps = [
-    ":content_shell_apk",
-  ]
+  data_deps = [ ":content_shell_apk" ]
   apk_under_test = ":content_shell_apk"
   apk_name = "ContentShellTest"
   android_manifest = "javatests/AndroidManifest.xml"
diff --git a/content/test/BUILD.gn b/content/test/BUILD.gn
index 0f1a6a8..6208f6a 100644
--- a/content/test/BUILD.gn
+++ b/content/test/BUILD.gn
@@ -6,7 +6,7 @@ import("//build/config/chrome_build.gni")
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
-import("//build/module_args/v8.gni")
+import("//build_overrides/v8.gni")
 import("//media/media_options.gni")
 import("//testing/test.gni")
 import("//third_party/mojo/src/mojo/public/tools/bindings/mojom.gni")
@@ -579,9 +579,7 @@ test("content_unittests") {
     ]
   }
 
-  data_deps = [
-    "//third_party/mesa:osmesa",
-  ]
+  data_deps = [ "//third_party/mesa:osmesa" ]
 
   if (!is_win) {
     sources += [ "../browser/file_descriptor_info_impl_unittest.cc" ]
diff --git a/gin/BUILD.gn b/gin/BUILD.gn
index 4535074..5dc1aa8 100644
--- a/gin/BUILD.gn
+++ b/gin/BUILD.gn
@@ -2,7 +2,7 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import("//build/module_args/v8.gni")
+import("//build_overrides/v8.gni")
 import("//testing/test.gni")
 
 component("gin") {
diff --git a/net/BUILD.gn b/net/BUILD.gn
index 0075633..319e1e7 100644
--- a/net/BUILD.gn
+++ b/net/BUILD.gn
@@ -7,7 +7,7 @@ import("//build/config/compiler/compiler.gni")
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
-import("//build/module_args/v8.gni")
+import("//build_overrides/v8.gni")
 import("//testing/test.gni")
 import("//third_party/icu/config.gni")
 import("//third_party/protobuf/proto_library.gni")