[turbofan] extend escape analysis to reduce CheckMaps

test/mjsunit/compiler/escape-analysis-13.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 --turbo --turbo-escape --turbo-experimental
+
+function f() {
+  var x = {};
+  x.a = "a";
+  x.b = "b";
+  assertEquals("a", x.a);
+  assertEquals("b", x.b);
+}
+f();
+f();
+% OptimizeFunctionOnNextCall(f);
+f();