Offchain execution extensions (#4145)

* Pass Extensions instead of individual objects.

* Move TransactionPool to a separate ExternalitiesExtension.

* Fix compilation.?

* Clean up.

* Refactor testing utilities.

* Add docs, fix tests.

* Fix doctest.

* Fix formatting and add some logs.

* Add some docs.

* Remove unused files.

substrate/primitives/sr-io/src/lib.rs

@@ -35,7 +35,10 @@ use rstd::ops::Deref;
 
 #[cfg(feature = "std")]
 use primitives::{
-	crypto::Pair, traits::KeystoreExt, offchain::OffchainExt, hexdisplay::HexDisplay,
+	crypto::Pair,
+	traits::KeystoreExt,
+	offchain::{OffchainExt, TransactionPoolExt},
+	hexdisplay::HexDisplay,
 	storage::ChildStorageKey,
 };
 
@@ -424,8 +427,9 @@ pub trait Offchain {
 	///
 	/// The transaction will end up in the pool.
 	fn submit_transaction(&mut self, data: Vec<u8>) -> Result<(), ()> {
-		self.extension::<OffchainExt>()
-			.expect("submit_transaction can be called only in the offchain worker context")
+		self.extension::<TransactionPoolExt>()
+			.expect("submit_transaction can be called only in the offchain call context with
+				TransactionPool capabilities enabled")
 			.submit_transaction(data)
 	}