Implementation of null-aware operators.

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

 // Copyright (c) 2013, 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 dart2js.ir_builder_task;
 
 import '../closure.dart' as closurelib;
 import '../closure.dart' hide ClosureScope;
 import '../constants/expressions.dart';
 import '../dart_types.dart';
@@ skipping 826 matching lines @@
 
     ir.Primitive buildRightValue(IrBuilder rightBuilder) {
       return withBuilder(rightBuilder, () => visit(right));
     }
 
     return irBuilder.buildLogicalOperator(
         leftValue, buildRightValue, isLazyOr: isLazyOr);
   }
 
   @override
+  ir.Primitive visitIfNull(
+      ast.Send node, ast.Node left, ast.Node right, _) {
+    internalError(node, "If-null not yet implemented in cps_ir");
+  }
+
+  @override
   ir.Primitive visitLogicalAnd(
       ast.Send node, ast.Node left, ast.Node right, _) {
     return translateLogicalOperator(left, right, isLazyOr: false);
   }
 
   @override
   ir.Primitive visitLogicalOr(
       ast.Send node, ast.Node left, ast.Node right, _) {
     return translateLogicalOperator(left, right, isLazyOr: true);
   }
@@ skipping 2216 matching lines @@
     node.body = replacementFor(node.body);
   }
 }
 
 /// Visit a just-deleted subterm and unlink all [Reference]s in it.
 class RemovalVisitor extends ir.RecursiveVisitor {
   processReference(ir.Reference reference) {
     reference.unlink();
   }
 }