[crankshaft] Always force number representation for increment.

test/mjsunit/regress/regress-664087.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
+
+function g() {
+  throw 1;
+}
+
+var v = { valueOf : g };
+
+function foo(v) {
+  v++;
+}
+
+%NeverOptimizeFunction(g);
+assertThrows(function () { foo(v); });
+assertThrows(function () { foo(v); });
+%OptimizeFunctionOnNextCall(foo);
+assertThrows(function () { foo(v); });