Add Chromium environment application test support.

mojo/public/cpp/application/BUILD.gn

Index: mojo/public/cpp/application/BUILD.gn
diff --git a/mojo/public/cpp/application/BUILD.gn b/mojo/public/cpp/application/BUILD.gn
index 83dc136c30df608e5e9c58b355f2b3238728daea..5d8fa0800e80f24580546c3b5185f803ee74f6cd 100644
--- a/mojo/public/cpp/application/BUILD.gn
+++ b/mojo/public/cpp/application/BUILD.gn
@@ -48,6 +48,11 @@ source_set("standalone") {
 
 source_set("test_support") {
   testonly = true
+  sources = [
+    "application_test_base.h",
+    "lib/application_test_base.cc",
+  ]
+
   deps = [
     ":application",
     "//mojo/public/cpp/bindings",
@@ -55,10 +60,11 @@ source_set("test_support") {
     "//mojo/public/cpp/system",
     "//testing/gtest",
   ]
+}
 
-  sources = [
-    "application_test_base.h",
-    "lib/application_test_base.cc",
-    "lib/application_test_main.cc",
-  ]
+source_set("test_support_standalone") {
+  testonly = true
+  sources = [ "lib/application_test_main.cc", ]
+  public_deps = [ ":test_support", ]
+  deps = [ "//mojo/public/cpp/environment:standalone", ]
 }