Move profiler code from util into a new crate profile.

- Most of util::memory has been moved into profile::mem, though the
  `SizeOf` trait and related things remain in util::memory. The
  `SystemMemoryReporter` code is now in a submodule
  profile::mem::system_reporter.

- util::time has been moved entirely into profile::time.

components/gfx/lib.rs

@@ -27,6 +27,7 @@ extern crate layers;
 extern crate libc;
 extern crate stb_image;
 extern crate png;
+extern crate profile;
 extern crate script_traits;
 extern crate "rustc-serialize" as rustc_serialize;
 extern crate unicode;