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

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

 library dart2js.cps_ir_integrity;
 
 import 'cps_ir_nodes.dart';
 import 'cps_ir_nodes_sexpr.dart';
 import '../tracer.dart' as tracer;
 
 /// Dump S-expressions on error if the tracer is enabled.
 ///
 /// Technically this has nothing to do with the tracer, but if you want one
 /// enabled, you typically want the other as well, so we use the same flag.
@@ skipping 84 matching lines @@
 
   @override
   visitLetMutable(LetMutable node) {
     markAsSeen(node.variable);
     processReference(node.value);
     doInScope([node.variable], node, () => visit(node.body));
   }
 
   @override
   visitFunctionDefinition(FunctionDefinition node) {
-    if (node.thisParameter != null) {
-      markAsSeen(node.thisParameter);
-    }
     node.parameters.forEach(markAsSeen);
     if (node.body != null) {
-      doInOptionalScope(node.thisParameter, node,
-          () => doInScope(node.parameters, node, () => visit(node.body)));
+      doInScope(node.parameters, node, () => visit(node.body));
     }
   }
 
   @override
   visitConstructorDefinition(ConstructorDefinition node) {
-    if (node.thisParameter != null) {
-      markAsSeen(node.thisParameter);
-    }
     node.parameters.forEach(markAsSeen);
     doInScope(node.parameters, node, () {
       if (node.initializers != null) node.initializers.forEach(visit);
-      if (node.body != null) {
-        doInOptionalScope(node.thisParameter, node, () => visit(node.body));
-      }
+      if (node.body != null) visit(node.body);
     });
   }
 
-  doInOptionalScope(Parameter parameter, Node node, action) {
-    return (parameter == null)
-        ? action()
-        : doInScope([parameter], node, action);
-  }
-
   @override
   visitDeclareFunction(DeclareFunction node) {
     markAsSeen(node.variable);
     doInScope([node.variable], node, () {
       visit(node.definition);
       visit(node.body);
     });
   }
 
   @override
@@ skipping 67 matching lines @@
   void check(ExecutableDefinition node) {
     topLevelNode = node;
     visit(node);
 
     // Check this last, so out-of-scope references are not classified as
     // a broken reference chain.
     seenDefinitions.forEach(checkReferenceChain);
   }
 
 }