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

mojo/public/c/environment/tests/BUILD.gn

Index: mojo/public/c/environment/tests/BUILD.gn
diff --git a/mojo/public/c/environment/tests/BUILD.gn b/mojo/public/c/environment/tests/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..0f7fb4e29375726f3fe66ef728e4e0915a87cc4b
--- /dev/null
+++ b/mojo/public/c/environment/tests/BUILD.gn
@@ -0,0 +1,20 @@
+# Copyright 2016 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import("../../../mojo_sdk.gni")
+
+mojo_sdk_source_set("perftest_helpers") {
+  testonly = true
+
+  sources = [
+    "async_waiter_perftest_helpers.cc",
+    "async_waiter_perftest_helpers.h",
+  ]
+
+  mojo_sdk_deps = [
+    "mojo/public/c/environment",
+    "mojo/public/c/system",
+    "mojo/public/cpp/system",
+  ]
+}