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

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

Index: pkg/compiler/lib/src/cps_ir/cps_ir_tracer.dart
diff --git a/pkg/compiler/lib/src/cps_ir/cps_ir_tracer.dart b/pkg/compiler/lib/src/cps_ir/cps_ir_tracer.dart
index 74c4b1ccd050593c8de79e009a4b5f1589b5df78..97314262323c6e1d92b1a87c2d2bd6c63280cae9 100644
--- a/pkg/compiler/lib/src/cps_ir/cps_ir_tracer.dart
+++ b/pkg/compiler/lib/src/cps_ir/cps_ir_tracer.dart
@@ -321,6 +321,10 @@ class IRTracer extends TracerUtil implements cps_ir.Visitor {
     return "Interceptor(${formatReference(node.input)})";
   }
 
+  visitThis(cps_ir.This node) {
+    return "This";
+  }
+
   visitReifyTypeVar(cps_ir.ReifyTypeVar node) {
     return "ReifyTypeVar ${node.typeVariable.name}";
   }
@@ -545,6 +549,9 @@ class BlockCollector implements cps_ir.Visitor {
   visitConstant(cps_ir.Constant node) {
     unexpectedNode(node);
   }
+  visitThis(cps_ir.This node) {
+    unexpectedNode(node);
+  }
   visitReifyTypeVar(cps_ir.ReifyTypeVar node) {
     unexpectedNode(node);
   }