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

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

 // Copyright (c) 2015, 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 builtin_operator;
 // This is shared by the CPS and Tree IRs.
 // Both cps_ir_nodes and tree_ir_nodes import and re-export this file.
 
 /// An operator supported natively in the CPS and Tree IRs using the
 /// `ApplyBuiltinOperator` instructions.
 ///
@@ skipping 115 matching lines @@
   /// The argument must be repeated 2 times.
   ///
   /// Compiles to `Math.floor(x) === x`
   IsFloor,
 
   /// Returns true if the argument is an integer.
   ///
   /// The argument must be repeated 3 times.
   ///
   /// 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.
   ///
   /// Precondition: Argument is a JavaScript Array.
   IsFixedLengthJSArray,
 
   // TODO(sra): Remove this and replace with IsFalsy(IsFixedLengthJSArray(x)).
   IsExtendableJSArray,
 
@@ skipping 41 matching lines @@
     case BuiltinOperator.NumSubtract:
     case BuiltinOperator.NumMultiply:
     case BuiltinOperator.NumDivide:
     case BuiltinOperator.NumRemainder:
     case BuiltinOperator.StringConcatenate:
       return true;
     default:
       return false;
   }
 }