cpsir: insert guard and force specialization for [] and []=

pkg/compiler/lib/src/cps_ir/builtin_operator.dart

Index: pkg/compiler/lib/src/cps_ir/builtin_operator.dart
diff --git a/pkg/compiler/lib/src/cps_ir/builtin_operator.dart b/pkg/compiler/lib/src/cps_ir/builtin_operator.dart
index 2db4ac5bf62d70ee7a348e735609df5152f1abfd..a0daf1b9971f390703c5892e3c1e1597631e9c0e 100644
--- a/pkg/compiler/lib/src/cps_ir/builtin_operator.dart
+++ b/pkg/compiler/lib/src/cps_ir/builtin_operator.dart
@@ -135,6 +135,13 @@ enum BuiltinOperator {
   /// Compiles to `typeof x === 'number' && Math.floor(x) === x`
   IsNumberAndFloor,

[asgerf, 2016/02/10 08:37:04]

Please rename this to IsInteger to be consistent.

[Siggi Cherem (dart-lang), 2016/02/12 00:14:00]

Technically I no longer need IsNotInteger, so I could remove it, but I left it
here (and rename this to IsInteger) so we get the negated expression from the
tree-ir logical tree rewrite.

Is it worth it? I'm happy to remove it if you prefer.

[asgerf, 2016/02/12 10:29:10]

No please leave it in. It's been bothering me that we could not negate it.

 
+  /// Returns true if the argument is not an integer.
+  ///
+  /// The argument must be repeated 3 times.
+  ///
+  /// Compiles to `typeof x !== 'number' || Math.floor(x) !== x`
+  IsNotInteger,
+
   /// Returns true if the argument is a fixed length Array.
   ///
   /// Uses one argument.