[turbofan] Ensure {CheckMaps} is not used accross mutations.

test/mjsunit/regress/regress-crbug-685506.js

+// Copyright 2017 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --allow-natives-syntax --noconcurrent-recompilation
+
+var a = {};
+
+function init() {
+  a = [];
+  for (var __v_1 = 0; __v_1 < 10016; __v_1++) {
+    a.push({});
+  }
+  a.map(function() {}) + "";
+}
+init();
+
+function foo() {
+  a.push((a + "!", 23));
+  return a;
+}
+assertEquals(23, foo()[10016]);
+assertEquals(23, foo()[10017]);
+assertEquals(23, foo()[10018]);
+%OptimizeFunctionOnNextCall(foo);
+assertEquals(23, foo()[10019]);