[turbofan] Add a Simplified::CheckMaps instruction.

src/compiler/operator-properties.cc

Index: src/compiler/operator-properties.cc
diff --git a/src/compiler/operator-properties.cc b/src/compiler/operator-properties.cc
index 7ea0405b97fede763feadab3c6fff88ea7589a0f..463d5026a823f4673c4bd2a5031b169eb1d38b17 100644
--- a/src/compiler/operator-properties.cc
+++ b/src/compiler/operator-properties.cc
@@ -95,6 +95,10 @@ int OperatorProperties::GetFrameStateInputCount(const Operator* op) {
     case IrOpcode::kJSLessThanOrEqual:
       return 2;
 
+    // TODO(titzer): is this necessary?
+    case IrOpcode::kCheckMaps:
+      return 1;
+
     default:
       return 0;
   }