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

pkg/compiler/lib/src/tree_ir/optimization/statement_rewriter.dart

 // Copyright (c) 2014, 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 tree_ir.optimization.statement_rewriter;
 
 import 'optimization.dart' show Pass;
 import '../tree_ir_nodes.dart';
 
 /**
@@ skipping 270 matching lines @@
   /// Returns true if [exp] has no side effects and has a constant value within
   /// any given activation of the enclosing method.
   bool isEffectivelyConstant(Expression exp) {
     // TODO(asgerf): Can be made more aggressive e.g. by checking conditional
     // expressions recursively. Determine if that is a valuable optimization
     // and/or if it is better handled at the CPS level.
     return exp is Constant ||
            exp is This ||
            exp is CreateInvocationMirror ||
            exp is InvokeStatic && exp.isEffectivelyConstant ||
+           exp is Interceptor ||
            exp is ApplyBuiltinOperator ||
            exp is VariableUse && constantEnvironment.containsKey(exp.variable);
   }
 
   /// True if [node] is an assignment that can be propagated as a constant.
   bool isEffectivelyConstantAssignment(Expression node) {
     return node is Assign &&
            node.variable.writeCount == 1 &&
            isEffectivelyConstant(node.value);
   }
@@ skipping 322 matching lines @@
   Expression visitTypeExpression(TypeExpression node) {
     _rewriteList(node.arguments);
     return node;
   }
 
   Expression visitCreateInvocationMirror(CreateInvocationMirror node) {
     _rewriteList(node.arguments);
     return node;
   }
 
+  Expression visitInterceptor(Interceptor node) {
+    node.input = visitExpression(node.input);
+    return node;
+  }
+
   /// True if [operator] is a binary operator that always has the same value
   /// if its arguments are swapped.
   bool isSymmetricOperator(BuiltinOperator operator) {
     switch (operator) {
       case BuiltinOperator.StrictEq:
       case BuiltinOperator.StrictNeq:
       case BuiltinOperator.LooseEq:
       case BuiltinOperator.LooseNeq:
       case BuiltinOperator.NumAnd:
       case BuiltinOperator.NumOr:
@@ skipping 390 matching lines @@
   IsVariableUsedVisitor(this.variable);
 
   visitVariableUse(VariableUse node) {
     if (node.variable == variable) {
       wasFound = true;
     }
   }
 
   visitInnerFunction(FunctionDefinition node) {}
 }