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

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 443e170e67e5c651c2f7c4539f69fb1de9b08c4f..4e6c64f497486cfa87f0870e3726cd65926a4bff 100644
--- a/pkg/compiler/lib/src/cps_ir/cps_ir_tracer.dart
+++ b/pkg/compiler/lib/src/cps_ir/cps_ir_tracer.dart
@@ -175,6 +175,13 @@ class IRTracer extends TracerUtil implements cps_ir.Visitor {
     printStmt(dummy, "InvokeConstructor $callName ($args) $kont");
   }
 
+  visitConcatenateStrings(cps_ir.ConcatenateStrings node) {
+    String dummy = names.name(node);
+    String args = node.arguments.map(formatReference).join(', ');
+    String kont = formatReference(node.continuation);
+    printStmt(dummy, "ConcatenateStrings ($args) $kont");
+  }
+
   visitThrow(cps_ir.Throw node) {
     String dummy = names.name(node);
     String value = formatReference(node.value);
@@ -506,6 +513,10 @@ class BlockCollector implements cps_ir.Visitor {
     addEdgeToContinuation(exp.continuation);
   }
 
+  visitConcatenateStrings(cps_ir.ConcatenateStrings exp) {
+    addEdgeToContinuation(exp.continuation);
+  }
+
   visitThrow(cps_ir.Throw exp) {
   }