[wasm] Unittest for Int64Lowering.

src/compiler/int64-lowering.cc

Index: src/compiler/int64-lowering.cc
diff --git a/src/compiler/int64-lowering.cc b/src/compiler/int64-lowering.cc
index c9c87b65d6de55807e5fa6a13afbe5bc232a3287..8d8073f5471b413b061bce26f36e36fa09c6f08d 100644
--- a/src/compiler/int64-lowering.cc
+++ b/src/compiler/int64-lowering.cc
@@ -209,6 +209,8 @@ void Int64Lowering::LowerNode(Node* node) {
           signature()->parameter_count()) {
         int old_index = ParameterIndexOf(node->op());
         int new_index = GetParameterIndexAfterLowering(signature(), old_index);
+        // TODO(ahaas): Use NodeProperties::ChangeOp here instead of allocating
+        // a new node.
         Node* low_node =
             graph()->NewNode(common()->Parameter(new_index), graph()->start());