Revert "Use an explicit 'this' parameter instead of 'This' nodes."

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

 // Copyright (c) 2012, 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.
 
 part of dart_backend;
 
 // TODO(ahe): This class is simply wrong.  This backend should use
 // elements when it can, not AST nodes.  Perhaps a [Map<Element,
 // TreeElements>] is what is needed.
 class ElementAst {
@@ skipping 149 matching lines @@
     // TODO(karlklose): enable type propagation for dart2dart when constant
     // types are correctly marked as instantiated (Issue 21880).
     TypePropagator typePropagator = new TypePropagator(
         context.dartTypes,
         context.constantSystem,
         new UnitTypeSystem(),
         context.internalError);
     applyCpsPass(typePropagator);
     applyCpsPass(new RedundantPhiEliminator());
     applyCpsPass(new ShrinkingReducer());
-    //print(cpsDefinition.accept(new SExpressionStringifier()));
 
     // Do not rewrite the IR after variable allocation.  Allocation
     // makes decisions based on an approximation of IR variable live
     // ranges that can be invalidated by transforming the IR.
     new cps_ir.RegisterAllocator(context.internalError).visit(cpsDefinition);
 
     tree_builder.Builder builder =
         new tree_builder.Builder(context.internalError);
     tree_ir.ExecutableDefinition treeDefinition = builder.build(cpsDefinition);
     assert(treeDefinition != null);
@@ skipping 382 matching lines @@
   }
 
   void traceGraph(String title, var irObject) {
     compiler.tracer.traceGraph(title, irObject);
   }
 
   DartTypes get dartTypes => compiler.types;
 
   InternalErrorFunction get internalError => compiler.internalError;
 }