Initialize 'next' variable in async rewrite when using yield in finally blocks.

pkg/compiler/lib/src/js/rewrite_async.dart

 // Copyright (c) 2015, 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 rewrite_async;
 
 // TODO(sigurdm): Throws in catch-handlers are handled wrong.
 // TODO(sigurdm): Avoid using variables in templates. It could blow up memory
 // use.
 
@@ skipping 772 matching lines @@
     inits.add(makeInit(gotoName, js.number(0)));
     if (isAsync) {
       inits.add(makeInit(completerName, new js.New(newCompleter, [])));
     } else if (isAsyncStar) {
       inits.add(makeInit(controllerName,
           new js.Call(newController, [new js.VariableUse(helperName)])));
     }
     if (hasTryBlocks) {
       inits.add(makeInit(handlerName, new js.LiteralNull()));
     }
-    if (hasJumpThroughFinally) {
+    if (hasJumpThroughFinally || analysis.hasYield) {
       inits.add(makeInit(nextName, null));
     }
     if (analysis.hasExplicitReturns && isAsync) {
       inits.add(makeInit(returnValueName, null));
     }
     if (analysis.hasThis && !isSyncStar) {
       // Sync* functions must remember `this` on the level of the outer
       // function.
       inits.add(makeInit(selfName, new js.This()));
     }
@@ skipping 942 matching lines @@
   Map<js.Node, js.Node> targets = new Map<js.Node, js.Node>();
   List<js.Node> loopsAndSwitches = new List<js.Node>();
   List<js.LabeledStatement> labelledStatements =
       new List<js.LabeledStatement>();
   Set<String> usedNames = new Set<String>();
 
   bool hasExplicitReturns = false;
 
   bool hasThis = false;
 
+  bool hasYield = false;
+
   // The function currently being analyzed.
   js.Fun currentFunction;
 
   // For error messages.
   final Function unsupported;
 
   PreTranslationAnalysis(void this.unsupported(js.Node node));
 
   bool visit(js.Node node) {
     bool containsAwait = node.accept(this);
@@ skipping 370 matching lines @@
   bool visitWhile(js.While node) {
     loopsAndSwitches.add(node);
     bool condition = visit(node.condition);
     bool body = visit(node.body);
     loopsAndSwitches.removeLast();
     return condition || body;
   }
 
   @override
   bool visitDartYield(js.DartYield node) {
+    hasYield = true;
     visit(node.expression);
     return true;
   }
 }