Put IR builder visitors in a different library than IrBuilder.

pkg/analyzer2dart/lib/src/cps_generator.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 analyzer2dart.cps_generator;
 
 import 'package:analyzer/analyzer.dart';
 
 import 'package:compiler/src/dart_types.dart' as dart2js;
 import 'package:compiler/src/elements/elements.dart' as dart2js;
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/generated/element.dart' as analyzer;
 
 import 'package:compiler/src/dart2jslib.dart'
     show DART_CONSTANT_SYSTEM;
 import 'package:compiler/src/cps_ir/cps_ir_nodes.dart' as ir;
 import 'package:compiler/src/cps_ir/cps_ir_builder.dart';
+import 'package:compiler/src/cps_ir/cps_ir_builder_task.dart';
 import 'package:compiler/src/universe/universe.dart';
 
 import 'semantic_visitor.dart';
 import 'element_converter.dart';
 import 'util.dart';
 import 'identifier_semantics.dart';
 
 /// Visitor that converts the AST node of an analyzer element into a CPS ir
 /// node.
 class CpsElementVisitor extends analyzer.SimpleElementVisitor<ir.Node> {
@@ skipping 558 matching lines @@
     irBuilder.buildTry(
         tryStatementInfo: new TryStatementInfo(),
         buildTryBlock: subbuild(node.body),
         catchClauseInfos: catchClauseInfos);
   }
 }
 
 class NullCapturedVariables extends DartCapturedVariables {
   NullCapturedVariables() : super(null);
 }