[crankshaft] Fix invalid ToNumber optimization.

test/mjsunit/regress/regress-crbug-590989-1.js

+// Copyright 2016 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
+
+var o = {}
+var p = {foo: 1.5}
+
+function g(x) { return x.foo === +x.foo; }
+
+assertEquals(false, g(o));
+assertEquals(false, g(o));
+%OptimizeFunctionOnNextCall(g);
+assertEquals(false, g(o));  // Still fine here.
+assertEquals(true, g(p));
+%OptimizeFunctionOnNextCall(g);
+assertEquals(false, g(o));  // Confused by type feedback.