Add a perf test for async wait and fix a bug in mojo::RunLoop.

mojo/BUILD.gn

Index: mojo/BUILD.gn
diff --git a/mojo/BUILD.gn b/mojo/BUILD.gn
index 603cf24e49452877e3037fe4e95a306047c8402a..20e4b27b6ae23090f8ef26d38646304956ef3863 100644
--- a/mojo/BUILD.gn
+++ b/mojo/BUILD.gn
@@ -112,6 +112,7 @@ group("public_tests") {
     # Perf tests:
     ":mojo_public_c_system_perftests",
     ":mojo_public_cpp_bindings_perftests",
+    ":mojo_public_cpp_environment_perftests",
   ]
 }
 
@@ -185,3 +186,10 @@ test("mojo_public_cpp_bindings_perftests") {
     "//mojo/public/cpp/bindings/tests:perftests",
   ]
 }
+
+test("mojo_public_cpp_environment_perftests") {
+  deps = [
+    "//mojo/edk/test:run_all_perftests",
+    "//mojo/public/cpp/environment/tests:perftests",
+  ]
+}