Fix Smi vs. HeapObject confusion in HConstants.

test/mjsunit/regress/regress-crbug-412215.js

+// Copyright 2014 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 dummy = {foo: "true"};
+
+var a = {y:0.5};
+a.y = 357;
+var b = a.y;
+
+var d;
+function f(  )  {
+  d = 357;
+  return {foo: b};
+}
+f();
+f();
+%OptimizeFunctionOnNextCall(f);
+var x = f();
+
+// With the bug, x is now an invalid object; the code below
+// triggers a crash.
+
+function g(obj) {
+  return obj.foo.length;
+}
+
+g(dummy);
+g(dummy);
+%OptimizeFunctionOnNextCall(g);
+g(x);