Add GN build file for ui/aura target.

Test plan:

Debug:

$ gn gen out/Debug_gn
$ ninja -C out/Debug_gn aura

Release:

$ gn gen out/Release_gn --args='is_debug=false'
$ ninja -C out/Release_gn aura

Android:

$ gn gen out/Debug_gn --args='os="android" cpu_arch="arm"'
$ ninja -C out/Debug_gn aura

BUG=None
TEST=see above.
R=brettw@chromium.org,scottmg@chromium.org
TBR=ben
NOTRY=true

Review URL: https://codereview.chromium.org/305293002

git-svn-id: http://src.chromium.org/svn/trunk/src/build@275607 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

config/linux/BUILD.gn

@@ -77,6 +77,10 @@ config("xext") {
   libs = [ "Xext" ]
 }
 
+config("xrandr") {
+  libs = [ "xrandr" ]
+}
+
 config("libcap") {
   libs = [ "cap" ]
 }