Import queue API revamp (#2856)

* ImportQueue methods are now mut

* Link methods are now mut

* Remove Arc from BasicSyncQueue

* Fix tests

* Remove BasicSyncQueue

* Change the import queue API

* Add buffered_link

* Remove obsolete tests

* Comments and style improvement pass

* Fix grandpa and comment cleanup

* Update core/consensus/common/src/import_queue.rs

Co-Authored-By: André Silva <andre.beat@gmail.com>

substrate/core/consensus/common/src/block_import.rs

@@ -195,7 +195,7 @@ pub trait JustificationImport<B: BlockT> {
 	type Error: ::std::error::Error + Send + 'static;
 
 	/// Called by the import queue when it is started.
-	fn on_start(&self, _link: &dyn crate::import_queue::Link<B>) { }
+	fn on_start(&self, _link: &mut dyn crate::import_queue::Link<B>) { }
 
 	/// Import a Block justification and finalize the given block.
 	fn import_justification(
@@ -211,7 +211,7 @@ pub trait FinalityProofImport<B: BlockT> {
 	type Error: std::error::Error + Send + 'static;
 
 	/// Called by the import queue when it is started.
-	fn on_start(&self, _link: &dyn crate::import_queue::Link<B>) { }
+	fn on_start(&self, _link: &mut dyn crate::import_queue::Link<B>) { }
 
 	/// Import a Block justification and finalize the given block. Returns finalized block or error.
 	fn import_finality_proof(

substrate/core/consensus/common/src/lib.rs

@@ -26,7 +26,7 @@
 // our error-chain could potentially blow up otherwise
 #![recursion_limit="128"]
 
-#[macro_use] extern crate crossbeam_channel;
+extern crate crossbeam_channel;
 #[macro_use] extern crate log;
 
 use std::sync::Arc;