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

pkg/compiler/lib/src/js_backend/codegen/codegen.dart

Index: pkg/compiler/lib/src/js_backend/codegen/codegen.dart
diff --git a/pkg/compiler/lib/src/js_backend/codegen/codegen.dart b/pkg/compiler/lib/src/js_backend/codegen/codegen.dart
index eb1e6994d4ea067c3c39c1f53e7eb9232c212d64..38caa31158da4a88de1d072d0d22d2cdcf0142bf 100644
--- a/pkg/compiler/lib/src/js_backend/codegen/codegen.dart
+++ b/pkg/compiler/lib/src/js_backend/codegen/codegen.dart
@@ -1123,8 +1123,10 @@ class CodeGenerator extends tree_ir.StatementVisitor
         return js.js('typeof # !== "number"', args);
       case BuiltinOperator.IsFloor:
         return js.js('Math.floor(#) === #', args);
-      case BuiltinOperator.IsNumberAndFloor:
+      case BuiltinOperator.IsInteger:
         return js.js('typeof # === "number" && Math.floor(#) === #', args);
+      case BuiltinOperator.IsNotInteger:
+        return js.js('typeof # !== "number" || Math.floor(#) !== #', args);
       case BuiltinOperator.IsFixedLengthJSArray:
         // TODO(sra): Remove boolify (i.e. !!).
         return js.js(r'!!#.fixed$length', args);