LibYuv GN: Add GN test targets.

libyuv.gni

Index: libyuv.gni
diff --git a/libyuv.gni b/libyuv.gni
new file mode 100644
index 0000000000000000000000000000000000000000..2f6930d76f20d11d2d1ddfc589cfe7f2ac643224
--- /dev/null
+++ b/libyuv.gni
@@ -0,0 +1,17 @@
+# Copyright 2016 The LibYuv Project Authors. All rights reserved.
+#
+# Use of this source code is governed by a BSD-style license
+# that can be found in the LICENSE file in the root of the source
+# tree. An additional intellectual property rights grant can be found
+# in the file PATENTS. All contributing project authors may
+# be found in the AUTHORS file in the root of the source tree.
+
+import("//build_overrides/build.gni")
+import("//build/config/arm.gni")
+
+declare_args() {
+  libyuv_include_tests = !build_with_chromium
+  libyuv_disable_jpeg = false
+  libyuv_use_neon = (current_cpu == "arm64" ||
+      (current_cpu == "arm" && (arm_use_neon || arm_optionally_use_neon)))
+}