dart2js cps: Redundant join elimination.

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 24fdebc7c04909ac93d3ec9905f428b3a5a8c376..0064b6bf0bc0ff25d28b9d1e1cb3d21df5754312 100644
--- a/pkg/compiler/lib/src/cps_ir/cps_ir_tracer.dart
+++ b/pkg/compiler/lib/src/cps_ir/cps_ir_tracer.dart
@@ -110,10 +110,8 @@ class IRTracer extends TracerUtil implements cps_ir.Visitor {
   visitLetCont(cps_ir.LetCont node) {
     if (IR_TRACE_LET_CONT) {
       String dummy = names.name(node);
-      for (cps_ir.Continuation continuation in node.continuations) {
-        String id = names.name(continuation);
-        printStmt(dummy, "LetCont $id = <$id>");
-      }
+      String ids = node.continuations.map(names.name).join(', ');
+      printStmt(dummy, "LetCont $ids");
     }
     visit(node.body);
   }