Add unit tests skeleton for the time profiler

This commit adds a test crate for the time profiler to `tests/unit/profile`. The
only unit test contained in this crate is a smoke test that the time profiler
thread can be created and destroyed. It serves as a place for adding new tests
in the future.

tests/unit/profile/time.rs

@@ -0,0 +1,15 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use profile::time;
+use profile_traits::time::ProfilerMsg;
+
+#[test]
+fn time_profiler_smoke_test() {
+    let chan = time::Profiler::create(None);
+    assert!(true, "Can create the profiler thread");
+
+    chan.send(ProfilerMsg::Exit);
+    assert!(true, "Can tell the profiler thread to exit");
+}