compositing: Fix a couple of bugs that prevented iframes from painting after navigation.
The first bug was that iframes were not reflowed in their parent DOM when the child page navigated. This is fixed by simply having the constellation notify the appropriate script thread when navigation occurs.
The second bug was that the compositor was unable to adjust the pipeline for existing iframe layers, only new ones. This patch adds logic to do that.
The third bug was that we have ad-hoc reflow calls throughout script/, and we didn't trigger any reflow from the code that dispatches the `load` event for the iframe so the test for the first two issues would always time out. The second commit adds another reflow call to do that, and also bites the bullet and adds a catch-all reflow (which does nothing if there's no dirty nodes in the document) at the return to the event loop.
Closes#8081.
Extension of #9285.
<!-- Reviewable:start -->
[<img src="https://reviewable.io/review_button.png" height=40 alt="Review on Reviewable"/>](https://reviewable.io/reviews/servo/servo/9421)
<!-- Reviewable:end -->
after navigation.
The first bug was that iframes were not reflowed in their parent DOM
when the child page navigated. This is fixed by simply having the
constellation notify the appropriate script thread when navigation
occurs.
The second bug was that the compositor was unable to adjust the pipeline
for existing iframe layers, only new ones. This patch adds logic to do
that.
Closes#8081.
Browser API: implement iframe.reload()
fixes#8575
The implementation is naive, and doesn't support the `hardreload` parameter.
And for the test, I'm not sure how else I can test the reload.
<!-- Reviewable:start -->
[<img src="https://reviewable.io/review_button.png" height=40 alt="Review on Reviewable"/>](https://reviewable.io/reviews/servo/servo/8618)
<!-- Reviewable:end -->
fix intermittent Option::unwrap in timers
fixes intermittent #8616
This intermittent indicates real problem in code.
Lets consider such code:
```javascript
// timer 1
setTimeout(function() {
//timer 2
setTimeout(function() {}, 0);
}, 0);
```
When we receive event to fire timer 1 it will be selected and extracted from active timers list in fire_timer function. During timer 1 handler execution we will schedule timer 2 and request timer event for it. But it will be executed during same fire_timer call because of 0 timeout. And as a result we will have empty timers list and expecting event for timer 2 that will crash in assert.
I'm not sure that all I've written is clear, but we have something like this:
```
install timer 1 -> [1] in timers list
push and expect timer event 1 -> expected_event=1
received timer event 1
fire_timer()
select timer 1 to execute -> [] in timers list
execute timer 1 handler
install timer 2 -> [2] in timers list
push and expect timer event 2 -> expected_event=2
select timer 2 to execute (because of 0 timeout) -> [] in tiemrs list
execute timer 2 handler
expected_event=2 is dangling
received timer event 2
fire_timer() -> BOOM
```
<!-- Reviewable:start -->
[<img src="https://reviewable.io/review_button.png" height=40 alt="Review on Reviewable"/>](https://reviewable.io/reviews/servo/servo/8768)
<!-- Reviewable:end -->
