Integrity checker for CPS and Tree IR.

pkg/compiler/lib/src/dart_backend/dart_backend.dart

Index: pkg/compiler/lib/src/dart_backend/dart_backend.dart
diff --git a/pkg/compiler/lib/src/dart_backend/dart_backend.dart b/pkg/compiler/lib/src/dart_backend/dart_backend.dart
index e498d5a1433e0d1ffa19b7e465d8402ba77aa798..cd832feecfe76f847e102134f5ca14d8253fd856 100644
--- a/pkg/compiler/lib/src/dart_backend/dart_backend.dart
+++ b/pkg/compiler/lib/src/dart_backend/dart_backend.dart
@@ -14,12 +14,16 @@ import '../tree/tree.dart';
 import '../cps_ir/cps_ir_nodes.dart' as cps_ir;
 import '../constants/expressions.dart';
 import '../cps_ir/optimizers.dart';
+import '../cps_ir/optimizers.dart' as cps_opt;
 import '../tree_ir/tree_ir_builder.dart' as tree_builder;
 import '../tree_ir/tree_ir_nodes.dart' as tree_ir;
 import '../util/util.dart';
 import '../mirror_renamer/mirror_renamer.dart';
 import '../tree_ir/optimization/optimization.dart'
     show LogicalRewriter, LoopRewriter, CopyPropagator, StatementRewriter;
+import '../tree_ir/optimization/optimization.dart' as tree_opt;
+import '../tree_ir/tree_ir_integrity.dart';
+import '../cps_ir/cps_ir_integrity.dart';
 import 'backend_ast_emitter.dart' as backend_ast_emitter;
 import 'backend_ast_nodes.dart' as backend_ast;
 import 'backend_ast_to_frontend_ast.dart' as backend2frontend;