servo: Merge #11270 - Remove ConstellationChan (from servo:ConstellationChan); r=asajeffrey

Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data:
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy --faster` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

Either:
- [ ] There are tests for these changes OR
- [x] These changes do not require tests because _____

Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process.

It's a pointless abstraction that propagates the obsolete chan terminology,
swaps the order in which the sender and receiver are returned, and hides a
source of panics.

Source-Repo: https://github.com/servo/servo
Source-Revision: 27c25e859a45c3d79c85e96b85ec5226a3231e10

servo/components/script/dom/htmlbodyelement.rs

@@ -15,7 +15,6 @@ use dom::eventtarget::EventTarget;
 use dom::htmlelement::HTMLElement;
 use dom::node::{Node, document_from_node, window_from_node};
 use dom::virtualmethods::VirtualMethods;
-use msg::constellation_msg::ConstellationChan;
 use script_traits::ScriptMsg as ConstellationMsg;
 use std::rc::Rc;
 use string_cache::Atom;
@@ -153,9 +152,8 @@ impl VirtualMethods for HTMLBodyElement {
         let window = window_from_node(self);
         let document = window.Document();
         document.set_reflow_timeout(time::precise_time_ns() + INITIAL_REFLOW_DELAY);
-        let ConstellationChan(ref chan) = *window.constellation_chan();
         let event = ConstellationMsg::HeadParsed;
-        chan.send(event).unwrap();
+        window.constellation_chan().send(event).unwrap();
     }
 
     fn parse_plain_attribute(&self, name: &Atom, value: DOMString) -> AttrValue {