Add block announce validator. (#3346)

* Add `BlockAnnounceValidator` trait.

* Add associated data to block announcement.

* Make tests compile.

* Move validator into `sync.rs`.

* Smaller changes.

* Update core/network/src/protocol.rs

Co-Authored-By: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

* Update core/network/src/protocol.rs

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Update core/network/src/test/sync.rs

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Formatting.

* Remove assoc. data from `BlockImportNotification`.

* Use `Option<Vec<u8>>` for associated data.

* Update core/network/src/protocol/sync.rs

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Fix type error.

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

@@ -35,6 +35,7 @@ use sr_primitives::traits::{Block as BlockT, DigestFor};
 use futures::prelude::*;
 pub use inherents::InherentData;
 
+pub mod block_validation;
 pub mod offline_tracker;
 pub mod error;
 pub mod block_import;
@@ -52,6 +53,21 @@ pub use block_import::{
 };
 pub use select_chain::SelectChain;
 
+/// Block status.
+#[derive(Debug, PartialEq, Eq)]
+pub enum BlockStatus {
+	/// Added to the import queue.
+	Queued,
+	/// Already in the blockchain and the state is available.
+	InChainWithState,
+	/// In the blockchain, but the state is not available.
+	InChainPruned,
+	/// Block or parent is known to be bad.
+	KnownBad,
+	/// Not in the queue or the blockchain.
+	Unknown,
+}
+
 /// Environment producer for a Consensus instance. Creates proposer instance and communication streams.
 pub trait Environment<B: BlockT> {
 	/// The proposer type this creates.