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/generated_content.rs b/components/layout/generated_content.rs
index 024d51b22fb..af710142446 100644
--- a/components/layout/generated_content.rs
+++ b/components/layout/generated_content.rs
@@ -152,7 +152,7 @@ impl<'a> ResolveGeneratedContent<'a> {
 
 impl<'a> InorderFlowTraversal for ResolveGeneratedContent<'a> {
     #[inline]
-    fn process(&mut self, flow: &mut Flow, level: u32) {
+    fn process(&mut self, flow: &mut dyn Flow, level: u32) {
         let mut mutator = ResolveGeneratedContentFragmentMutator {
             traversal: self,
             level: level,
@@ -163,7 +163,7 @@ impl<'a> InorderFlowTraversal for ResolveGeneratedContent<'a> {
     }
 
     #[inline]
-    fn should_process_subtree(&mut self, flow: &mut Flow) -> bool {
+    fn should_process_subtree(&mut self, flow: &mut dyn Flow) -> bool {
         flow.base()
             .restyle_damage
             .intersects(ServoRestyleDamage::RESOLVE_GENERATED_CONTENT) ||