Add Ozone configuration to facilitate management of external platforms

ui/ozone/ozone_extra.gni

Index: ui/ozone/ozone_extra.gni
diff --git a/ui/ozone/ozone_extra.gni b/ui/ozone/ozone_extra.gni
new file mode 100644
index 0000000000000000000000000000000000000000..24ed364d86949c5d5ddac33a29ee75f1fc6176d3
--- /dev/null
+++ b/ui/ozone/ozone_extra.gni
@@ -0,0 +1,19 @@
+# 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.
+
+# This list contains the name of external platforms that are passed to the
+# --ozone-platform command line argument or used for the ozone_platform build
+# config. For example ozone_external_platforms = [ "foo1", "foo2", ... ]
+ozone_external_platforms = []
+
+# This list contains dependencies for your external platforms. Typically, the
+# Ozone implementations are placed into ui/ozone/platform/ and so this will
+# look something like:
+# ozone_external_platform_deps = [ "platform/foo1", "platform/foo_2", ... ]
+ozone_external_platform_deps = []
+
+# If your platform has unit tests, you can list the corresponding source_set

[tonikitoo, 2016/10/31 02:51:02]

I would write it in 3rd person:

"if a platform has unit tests, the corresponding source_set can be listed here
so that..."

+# here so that they get included into ozone_unittests.
+# ozone_external_platform_test_deps = [ "platform/foo1:foo1_unitests", ... ]
+ozone_external_platform_test_deps = []