Add lots of testonly annotations to the GN build.

ui/aura/BUILD.gn

Index: ui/aura/BUILD.gn
diff --git a/ui/aura/BUILD.gn b/ui/aura/BUILD.gn
index b5f08499f5b74c8470f3b745fffd907f5e65abe6..e90651c0e954b1bebc8c9f1ac127151ef7e6db2c 100644
--- a/ui/aura/BUILD.gn
+++ b/ui/aura/BUILD.gn
@@ -142,6 +142,7 @@ component("aura") {
 }
 
 source_set("test_support") {
+  testonly = true
   sources = [
     "test/aura_test_base.cc",
     "test/aura_test_base.h",
@@ -208,6 +209,8 @@ source_set("test_support") {
 
 executable("demo") {
   output_name = "aura_demo"
+  testonly = true
+
   sources = [
     "demo/demo_main.cc",
   ]
@@ -237,6 +240,8 @@ executable("demo") {
 
 executable("bench") {
   output_name = "aura_bench"
+  testonly = true
+
   sources = [
     "bench/bench_main.cc",
   ]