Introduce 'NullCompositor'.

src/components/main/compositing/mod.rs

@@ -197,7 +197,8 @@ impl CompositorTask {
                                           profiler_chan);
             }
             Headless => {
-                run_headless::run_compositor(&constellation_chan, port);
+                run_headless::NullCompositor::create(port,
+                                                     constellation_chan.clone());
             }
         }
 

src/components/main/compositing/run_headless.rs

@@ -8,34 +8,55 @@ use geom::size::Size2D;
 use servo_msg::constellation_msg::{ConstellationChan, ResizedWindowMsg};
 use std::comm::Port;
 
+
 /// Starts the compositor, which listens for messages on the specified port.
 ///
 /// This is the null compositor which doesn't draw anything to the screen.
 /// It's intended for headless testing.
-pub fn run_compositor(constellation_chan: &ConstellationChan, port: Port<Msg>) {
-    // Tell the constellation about the initial fake size.
-    constellation_chan.send(ResizedWindowMsg(Size2D(640u, 480u)));
+pub struct NullCompositor {
+    /// The port on which we receive messages.
+    port: Port<Msg>,
+}
 
-    loop {
-        match port.recv() {
-            Exit => break,
+impl NullCompositor {
 
-            GetGraphicsMetadata(chan) => {
-                chan.send(None);
+    fn new(port: Port<Msg>) -> NullCompositor {
+
+        NullCompositor {
+            port: port
+        }
+    }
+
+    pub fn create(port: Port<Msg>, constellation_chan: ConstellationChan) {
+        let compositor = NullCompositor::new(port);
+
+        // Tell the constellation about the initial fake size.
+        constellation_chan.send(ResizedWindowMsg(Size2D(640u, 480u)));
+        compositor.handle_message();
+    }
+
+    fn handle_message(&self) {
+        loop {
+            match self.port.recv() {
+                Exit => break,
+
+                GetGraphicsMetadata(chan) => {
+                    chan.send(None);
+                }
+
+                SetIds(_, response_chan, _) => {
+                    response_chan.send(());
+                }
+
+                // Explicitly list ignored messages so that when we add a new one,
+                // we'll notice and think about whether it needs a response, like
+                // SetIds.
+
+                NewLayer(*) | SetLayerPageSize(*) | SetLayerClipRect(*) | DeleteLayer(*) |
+                Paint(*) | InvalidateRect(*) | ChangeReadyState(*) | ChangeRenderState(*)|
+                ScrollFragmentPoint(*) | SetUnRenderedColor(*)
+                    => ()
             }
-
-            SetIds(_, response_chan, _) => {
-                response_chan.send(());
-            }
-
-            // Explicitly list ignored messages so that when we add a new one,
-            // we'll notice and think about whether it needs a response, like
-            // SetIds.
-
-            NewLayer(*) | SetLayerPageSize(*) | SetLayerClipRect(*) | DeleteLayer(*) |
-            Paint(*) | InvalidateRect(*) | ChangeReadyState(*) | ChangeRenderState(*)|
-            ScrollFragmentPoint(*) | SetUnRenderedColor(*)
-                => ()
         }
     }
 }