Revert "Allow LetCont to bind multiple continuations."

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

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library dart2js.ir_tracer;
 
 import 'dart:async' show EventSink;
 
 import 'cps_ir_nodes.dart' as cps_ir hide Function;
 import '../tracer.dart';
@@ skipping 94 matching lines @@
 
   visitLetPrim(cps_ir.LetPrim node) {
     String id = names.name(node.primitive);
     printStmt(id, "LetPrim $id = ${formatPrimitive(node.primitive)}");
     visit(node.body);
   }
 
   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 id = names.name(node.continuation);
+      printStmt(dummy, "LetCont $id = <$id>");
     }
     visit(node.body);
   }
 
   visitInvokeStatic(cps_ir.InvokeStatic node) {
     String dummy = names.name(node);
     String callName = node.selector.name;
     String args = node.arguments.map(formatReference).join(', ');
     String kont = formatReference(node.continuation);
     printStmt(dummy, "InvokeStatic $callName ($args) $kont");
@@ skipping 288 matching lines @@
 
   visitConstructorDefinition(cps_ir.ConstructorDefinition node) {
     visitExecutableDefinition(node);
   }
 
   visitLetPrim(cps_ir.LetPrim exp) {
     visit(exp.body);
   }
 
   visitLetCont(cps_ir.LetCont exp) {
-    exp.continuations.forEach(visit);
+    visit(exp.continuation);
     visit(exp.body);
   }
 
   void addEdgeToContinuation(cps_ir.Reference continuation) {
     cps_ir.Definition target = continuation.definition;
     if (target is cps_ir.Continuation && !target.isReturnContinuation) {
       current_block.addEdgeTo(getBlock(target));
     }
   }
 
@@ skipping 40 matching lines @@
     }
   }
 
   visitContinuation(cps_ir.Continuation c) {
     var old_node = current_block;
     current_block = getBlock(c);
     visit(c.body);
     current_block = old_node;
   }
 }