Copy the necessary build overrides from Chromium

build.gni

Index: build.gni
diff --git a/build.gni b/build.gni
new file mode 100644
index 0000000000000000000000000000000000000000..482116ca6f1b068c6a9dfcad0a71acee89a66efa
--- /dev/null
+++ b/build.gni
@@ -0,0 +1,15 @@
+# Copyright 2016 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.
+

[Roland McGrath, 2016/04/29 22:25:12]

I assume this file is copied verbatim from the chromium version.
There should be some kind of comment somewhere saying explicitly which files
were copied verbatim from where, and making clear that we should be manually
tracking these files in chromium to keep the copies here matching whenever we
update DEPS for build/ et al.  It's probably better to keep the copied file
itself verbatim so it can be updated with a simple cp.  So perhaps add a README
of some sort to the directory.

[Petr Hosek, 2016/04/29 22:36:54]

Done.

+# See https://bugs.chromium.org/p/webrtc/issues/detail?id=5453.
+# Some WebRTC targets require the 10.7 deployment version of the Mac SDK
+# and a 10.11 min SDK, but those targets are only used in non-Chromium
+# builds. We can remove this when Chromium drops 10.6 support and also
+# requires 10.7.
+mac_sdk_min_build_override = "10.10"
+mac_deployment_target_build_override = "10.7"
+
+# Variable that can be used to support multiple build scenarios, like having
+# Chromium specific targets in a client project's GN file etc.
+build_with_chromium = true