Make sure we're not trying to optimize an int check if the input can be a number.

tests/compiler/dart2js/simple_inferrer_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:expect/expect.dart';
 import
     '../../../sdk/lib/_internal/compiler/implementation/types/types.dart'
     show TypeMask;
 
 import 'compiler_helper.dart';
 import 'parser_helper.dart';
 
 const String TEST = """
 returnNum1(a) {
   if (a) return 1;
-  else return 2.0;
+  else return 2.5;
 }
 
 returnNum2(a) {
-  if (a) return 1.0;
+  if (a) return 1.4;
   else return 2;
 }
 
 returnInt1(a) {
   if (a) return 1;
   else return 2;
 }
 
 returnDouble(a) {
-  if (a) return 1.0;
-  else return 2.0;
+  if (a) return 1.5;
+  else return 2.5;
 }
 
 returnGiveUp(a) {
   if (a) return 1;
   else return 'foo';
 }
 
 returnInt2() {
   var a = 42;
   return a++;
@@ skipping 668 matching lines @@
   }
   checkFactoryConstructor('A', '');
 
   checkReturn('testCascade1', typesTask.growableListType);
   checkReturn('testCascade2', new TypeMask.nonNullExact(
       typesTask.rawTypeOf(findElement(compiler, 'CascadeHelper'))));
   checkReturn('testSpecialization1', typesTask.numType);
   checkReturn('testSpecialization2', typesTask.dynamicType);
   checkReturn('testSpecialization3', typesTask.intType.nullable());
 }