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, 3 insertions, 3 deletions

diff --git a/components/layout/context.rs b/components/layout/context.rs
index 1ab4637cd8a..08530e74a5c 100644
--- a/components/layout/context.rs
+++ b/components/layout/context.rs
@@ -64,7 +64,7 @@ pub struct LayoutContext<'a> {
     pub style_context: SharedStyleContext<'a>,
 
     /// Reference to the script thread image cache.
-    pub image_cache: Arc<ImageCache>,
+    pub image_cache: Arc<dyn ImageCache>,
 
     /// Interface to the font cache thread.
     pub font_cache_thread: Mutex<FontCacheThread>,
@@ -77,7 +77,7 @@ pub struct LayoutContext<'a> {
     >,
 
     /// Paint worklets
-    pub registered_painters: &'a RegisteredPainters,
+    pub registered_painters: &'a dyn RegisteredPainters,
 
     /// A list of in-progress image loads to be shared with the script thread.
     /// A None value means that this layout was not initiated by the script thread.
@@ -197,5 +197,5 @@ pub trait RegisteredPainter: RegisteredSpeculativePainter + Painter {}
 /// A set of registered painters
 pub trait RegisteredPainters: Sync {
     /// Look up a painter
-    fn get(&self, name: &Atom) -> Option<&RegisteredPainter>;
+    fn get(&self, name: &Atom) -> Option<&dyn RegisteredPainter>;
 }