Auto merge of #22133 - servo:extern-crate, r=SimonSapin

Use 2018-edition idioms in crates that use that edition

The first commit is almost entirely mechanical, created by running `cargo fix --edition-idioms` and relevant crates. I undid the change of adding an anonymous lifetime parameter in types that have implicit lifetimes parameters, for example replacing `&mut Formatter` with `&mut Formatter<'_>`, because I don’t like it. The remaining changes are, in many places:

* Add `dyn` to trait object types, for example `Rc<gl::Gl>` to `Rc<dyn gl::Gl>`. This change also works in the 2015 edition.
* Remove `extern crate` where is it made unneeded by changes to the import/module system.

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1 files changed, 2 insertions, 2 deletions

diff --git a/components/layout/incremental.rs b/components/layout/incremental.rs
index 6734620e5a0..7dde93384b7 100644
--- a/components/layout/incremental.rs
+++ b/components/layout/incremental.rs
@@ -27,7 +27,7 @@ pub trait LayoutDamageComputation {
     fn reflow_entire_document(self);
 }
 
-impl<'a> LayoutDamageComputation for &'a mut Flow {
+impl<'a> LayoutDamageComputation for &'a mut dyn Flow {
     fn compute_layout_damage(self) -> SpecialRestyleDamage {
         let mut special_damage = SpecialRestyleDamage::empty();
         let is_absolutely_positioned = self
@@ -53,7 +53,7 @@ impl<'a> LayoutDamageComputation for &'a mut Flow {
                         .damage_for_child(is_absolutely_positioned, child_is_absolutely_positioned),
                 );
                 {
-                    let kid: &mut Flow = kid;
+                    let kid: &mut dyn Flow = kid;
                     special_damage.insert(kid.compute_layout_damage());
                 }
                 self_base.restyle_damage.insert(