Partial support for events in WebXR

[Manishearth]

Needs servo/webxr#20

r? @asajeffrey

---

This change is 

[highfive]

Heads up! This PR modifies the following files:

• @asajeffrey: components/script/dom/xrrenderstate.rs, components/script/dom/webidls/XRSession.webidl, components/script/dom/xrwebgllayer.rs, components/script/dom/xrtest.rs, components/script/dom/webidls/XRLayer.webidl and 9 more
• @KiChjang: components/script/dom/xrrenderstate.rs, components/script/dom/webidls/XRSession.webidl, components/script/dom/xrwebgllayer.rs, components/script/dom/xrtest.rs, components/script/dom/webidls/XRLayer.webidl and 9 more

[asajeffrey]

Looks good!

[asajeffrey]

Hmm, we're dup'ing euclid now? Hopefully the dupe police on onto this!

[Manishearth]

cc @Eijebong

[asajeffrey]

This is much nicer now we don't have XRLayer!

[Manishearth]

yay

[Manishearth]

@bors-servo r=asajeffrey

[bors-servo]

📌 Commit c4ac61c has been approved by asajeffrey

[bors-servo]

⌛ Testing commit c4ac61c with merge 3d9dbbf...

[CYBAI]

Diff in /repo/components/script/dom/xrsession.rs at line 395:
         // shuts itself down
         self.ended.set(true);
         global.as_window().Navigator().Xr().end_session(self);
�[31m-        self.session
�(B�[m�[31m-            .borrow_mut()
�(B�[m�[31m-            .end_session();
�(B�[m�[32m+        self.session.borrow_mut().end_session();
�(B�[m         p
     }
 }
Run `./mach fmt` to fix the formatting

[bors-servo]

💔 Test failed - linux-rel-wpt

[Manishearth]

@bors-servo r=asajeffrey

[bors-servo]

📌 Commit 3f95d30 has been approved by asajeffrey

[bors-servo]

⌛ Testing commit 3f95d30 with merge 7afe215...

[jdm]

{
    "status": "TIMEOUT", 
    "group": "default", 
    "message": "Test timed out", 
    "stack": null, 
    "subtest": "Calling end during an input callback stops processing at the right time", 
    "test": "/webxr/xrSession_input_events_end.https.html", 
    "line": 50304, 
    "action": "test_result", 
    "expected": "FAIL"
}
{
    "status": "TIMEOUT", 
    "group": "default", 
    "message": null, 
    "stack": null, 
    "subtest": null, 
    "test": "/webxr/xrSession_input_events_end.https.html", 
    "line": 50305, 
    "action": "test_result", 
    "expected": "ERROR"
}

[jdm]

Looks like the same failure mode as #23796

[bors-servo]

☀️ Test successful - linux-rel-css, linux-rel-wpt, status-taskcluster
Approved by: asajeffrey
Pushing 7afe215 to master...