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

tests/compiler/dart2js/mock_compiler.dart

 // Copyright (c) 2012, 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.
 
 library mock_compiler;
 
 import "package:expect/expect.dart";
 import 'dart:collection';
 
 import '../../../sdk/lib/_internal/compiler/compiler.dart' as api;
@@ skipping 105 matching lines @@
   class JSFixedArray extends JSMutableArray {}
   class JSExtendableArray extends JSMutableArray {}
   class JSString extends Interceptor implements String, JSIndexable {
     var length;
     operator[](index) {}
     toString() {}
     operator+(other) => this;
   }
   class JSNumber extends Interceptor implements num {
     // All these methods return a number to please type inferencing.
-    operator-() => (this is JSInt) ? 42 : 42.0;
-    operator +(other) => (this is JSInt) ? 42 : 42.0;
-    operator -(other) => (this is JSInt) ? 42 : 42.0;
+    operator-() => (this is JSInt) ? 42 : 42.2;
+    operator +(other) => (this is JSInt) ? 42 : 42.2;
+    operator -(other) => (this is JSInt) ? 42 : 42.2;
     operator ~/(other) => 42;
-    operator /(other) => (this is JSInt) ? 42 : 42.0;
-    operator *(other) => (this is JSInt) ? 42 : 42.0;
-    operator %(other) => (this is JSInt) ? 42 : 42.0;
+    operator /(other) => (this is JSInt) ? 42 : 42.2;
+    operator *(other) => (this is JSInt) ? 42 : 42.2;
+    operator %(other) => (this is JSInt) ? 42 : 42.2;
     operator <<(other) => 42;
     operator >>(other) => 42;
     operator |(other) => 42;
     operator &(other) => 42;
     operator ^(other) => 42;
 
     operator >(other) => true;
     operator >=(other) => true;
     operator <(other) => true;
     operator <=(other) => true;
     operator ==(other) => true;
     get hashCode => throw "JSNumber.hashCode not implemented.";
 
-    abs() => (this is JSInt) ? 42 : 42.0;
-    remainder(other) => (this is JSInt) ? 42 : 42.0;
+    abs() => (this is JSInt) ? 42 : 42.2;
+    remainder(other) => (this is JSInt) ? 42 : 42.2;
     truncate() => 42;
   }
   class JSInt extends JSNumber implements int {
   }
   class JSDouble extends JSNumber implements double {
   }
   class JSNull extends Interceptor {
     bool operator==(other) => identical(null, other);
     get hashCode => throw "JSNull.hashCode not implemented.";
     String toString() => 'Null';
@@ skipping 302 matching lines @@
   }
 }
 
 class MockDeferredLoadTask extends DeferredLoadTask {
   MockDeferredLoadTask(Compiler compiler) : super(compiler);
 
   void registerMainApp(LibraryElement mainApp) {
     // Do nothing.
   }
 }