Remove use of CCoinsViewMemPool::GetCoin in wallet code

This commit does not change behavior.

src/node/coin.cpp

@@ -0,0 +1,22 @@
+// Copyright (c) 2019 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <node/coin.h>
+
+#include <txmempool.h>
+#include <validation.h>
+
+void FindCoins(std::map<COutPoint, Coin>& coins)
+{
+    LOCK2(cs_main, ::mempool.cs);
+    assert(pcoinsTip);
+    CCoinsViewCache& chain_view = *::pcoinsTip;
+    CCoinsViewMemPool mempool_view(&chain_view, ::mempool);
+    for (auto& coin : coins) {
+        if (!mempool_view.GetCoin(coin.first, coin.second)) {
+            // Either the coin is not in the CCoinsViewCache or is spent. Clear it.
+            coin.second.Clear();
+        }
+    }
+}

src/node/coin.h

@@ -0,0 +1,22 @@
+// Copyright (c) 2019 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_NODE_COIN_H
+#define BITCOIN_NODE_COIN_H
+
+#include <map>
+
+class COutPoint;
+class Coin;
+
+/**
+ * Look up unspent output information. Returns coins in the mempool and in the
+ * current chain UTXO set. Iterates through all the keys in the map and
+ * populates the values.
+ *
+ * @param[in,out] coins map to fill
+ */
+void FindCoins(std::map<COutPoint, Coin>& coins);
+
+#endif // BITCOIN_NODE_COIN_H