Begin threading execution layer into BeaconChain

beacon_node/beacon_chain/src/beacon_chain.rs

@@ -46,6 +46,7 @@ use crate::BeaconForkChoiceStore;
 use crate::BeaconSnapshot;
 use crate::{metrics, BeaconChainError};
 use eth2::types::{EventKind, SseBlock, SseChainReorg, SseFinalizedCheckpoint, SseHead, SyncDuty};
+use execution_layer::ExecutionLayer;
 use fork_choice::ForkChoice;
 use futures::channel::mpsc::Sender;
 use itertools::process_results;
@@ -272,6 +273,8 @@ pub struct BeaconChain<T: BeaconChainTypes> {
         Mutex<ObservedOperations<AttesterSlashing<T::EthSpec>, T::EthSpec>>,
     /// Provides information from the Ethereum 1 (PoW) chain.
     pub eth1_chain: Option<Eth1Chain<T::Eth1Chain, T::EthSpec>>,
+    /// Interfaces with the execution client.
+    pub execution_layer: Option<ExecutionLayer>,
     /// Stores a "snapshot" of the chain at the time the head-of-the-chain block was received.
     pub(crate) canonical_head: TimeoutRwLock<BeaconSnapshot<T::EthSpec>>,
     /// The root of the genesis block.