Remove the fake memory profiler thread.

Currently if you don't specify the '-m' option, a fake do-nothing memory
profiler thread gets created instead of the real one. It ignores all
events except for `Exit`. And the timer thread doesn't get created so no
`Print` events are sent.

This changeset instead always creates the real thread. If you specify
'-m' the *timer* thread is still absent and it won't print anything.
However, the memory profiler thread will respond to register/unregister
events, which is good, because if there's a bug in those (e.g.
double-registration of a particular name) it'll show up in invocations
that lack '-m'.

components/util/memory.rs

@@ -243,37 +243,27 @@ pub struct MemoryProfiler {
 impl MemoryProfiler {
     pub fn create(period: Option<f64>) -> MemoryProfilerChan {
         let (chan, port) = channel();
-        match period {
+
-            Some(period) => {
+        // Create the timer thread if a period was provided.
-                let period = Duration::milliseconds((period * 1000f64) as i64);
+        if let Some(period) = period {
+            let period_ms = Duration::milliseconds((period * 1000f64) as i64);
             let chan = chan.clone();
             spawn_named("Memory profiler timer".to_owned(), move || {
                 loop {
-                        sleep(period);
+                    sleep(period_ms);
                     if chan.send(MemoryProfilerMsg::Print).is_err() {
                         break;
                     }
                 }
             });
-                // Spawn the memory profiler.
+        }
+
+        // Always spawn the memory profiler. If there is no timer thread it won't receive regular
+        // `Print` events, but it will still receive the other events.
         spawn_named("Memory profiler".to_owned(), move || {
             let mut memory_profiler = MemoryProfiler::new(port);
             memory_profiler.start();
         });
-            }
-            None => {
-                // No-op to handle messages when the memory profiler is
-                // inactive.
-                spawn_named("Memory profiler".to_owned(), move || {
-                    loop {
-                        match port.recv() {
-                            Err(_) | Ok(MemoryProfilerMsg::Exit) => break,
-                            _ => {}
-                        }
-                    }
-                });
-            }
-        }
 
         MemoryProfilerChan(chan)
     }