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

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 1258 matching lines @@
 
   List<ir.Primitive> normalizeDynamicArguments(
       Selector selector,
       List<ir.Primitive> arguments) {
     return arguments;
   }
 
   @override
   ir.Primitive buildReifyTypeVariable(ir.Primitive target,
                                       TypeVariableType variable) {
-    assert(target is ir.This);
+    //assert(target == irBuilder.state.thisParameter);
+    assert(target == irBuilder.state.enclosingMethodThisParameter);
     ir.Primitive prim = new ir.ReifyTypeVar(variable.element);
     irBuilder.add(new ir.LetPrim(prim));
     return prim;
   }
 }
 
 /// IR builder specific to the JavaScript backend, coupled to the [JsIrBuilder].
 class JsIrBuilderVisitor extends IrBuilderVisitor {
   /// Promote the type of [irBuilder] to [JsIrBuilder].
   JsIrBuilder get irBuilder => super.irBuilder;
@@ skipping 561 matching lines @@
   SourceInformation buildCall(ast.Node node) {
     return new PositionSourceInformation(
         new TokenSourceLocation(sourceFile, node.getBeginToken(), name));
   }
 
   @override
   SourceInformationBuilder forContext(AstElement element) {
     return new PositionSourceInformationBuilder(element);
   }
 }