Revert "dart2js cps: Refactor and optimize string concatenations."

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

Index: pkg/compiler/lib/src/cps_ir/cps_ir_nodes_sexpr.dart
diff --git a/pkg/compiler/lib/src/cps_ir/cps_ir_nodes_sexpr.dart b/pkg/compiler/lib/src/cps_ir/cps_ir_nodes_sexpr.dart
index 7106756bf6cb81cbb929cf1611ba88797a8d1438..f287c4d7ef07dc5408d779d53cc9f924fb6b50fe 100644
--- a/pkg/compiler/lib/src/cps_ir/cps_ir_nodes_sexpr.dart
+++ b/pkg/compiler/lib/src/cps_ir/cps_ir_nodes_sexpr.dart
@@ -173,6 +173,12 @@ class SExpressionStringifier extends Indentation implements Visitor<String> {
     return '$indentation(InvokeConstructor $callName $args $cont)';
   }
 
+  String visitConcatenateStrings(ConcatenateStrings node) {
+    String cont = access(node.continuation);
+    String args = node.arguments.map(access).join(' ');
+    return '$indentation(ConcatenateStrings ($args) $cont)';
+  }
+
   String visitInvokeContinuation(InvokeContinuation node) {
     String name = access(node.continuation);
     if (node.isRecursive) name = 'rec $name';