dart2js cps: Make Identical a built-in and add Interceptor to Tree IR.

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 29 matching lines @@
   /// Concatenates any number of strings.
   ///
   /// Takes any number of arguments, and each argument must be a string.
   ///
   /// Returns the empty string if no arguments are given.
   StringConcatenate,
 
   /// Returns true if the two arguments are the same value, and that value is
   /// not NaN, or if one argument is +0 and the other is -0.
   ///
-  /// At most one of the arguments may be null.
+  /// Compiled as a static method call.
+  Identical,
+
+  /// Like [Identical], except at most one argument may be null.
+  ///
+  /// Compiles to `===`.
   StrictEq,
 
   /// Negated version of [StrictEq]. Introduced by [LogicalRewriter] in Tree IR.
   StrictNeq,
 
   /// Returns true if the two arguments are both null or are the same string,
   /// boolean, or number, and that number is not NaN, or one argument is +0
   /// and the other is -0.
   ///
   /// One of the following must hold:
   /// - At least one argument is null.
   /// - Arguments are both strings, or both booleans, or both numbers.
+  ///
+  /// Compiles to `==`.
   LooseEq,
 
   /// Negated version of [LooseEq]. Introduced by [LogicalRewriter] in Tree IR.
   LooseNeq,
 
   /// Returns true if the argument is false, +0. -0, NaN, the empty string,
   /// or null.
+  ///
+  /// Compiles to `!`.
   IsFalsy,
 
   /// Returns true if the argument is a number.
   ///
   /// Compiles to `typeof x === 'number'`
   IsNumber,
 
   /// Returns true if the argument is not a number.
   ///
   /// Compiles to `typeof x !== 'number'`.
   IsNotNumber,
 
   /// Returns true if the argument is an integer, false if it is a double or
   /// null, and unspecified if it is anything else.
   ///
   /// 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,
 }