Make await for cancel the stream when breaking out of the loop

runtime/vm/ast.h

 // Copyright (c) 2012, 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.
 
 #ifndef VM_AST_H_
 #define VM_AST_H_
 
 #include "platform/assert.h"
 #include "vm/allocation.h"
 #include "vm/growable_array.h"
@@ skipping 1838 matching lines @@
                SequenceNode* finally_block,
                intptr_t try_index)
       : AstNode(token_pos),
         try_block_(try_block),
         context_var_(*context_var),
         catch_block_(catch_block),
         finally_block_(finally_block),
         try_index_(try_index) {
     ASSERT(try_block_ != NULL);
     ASSERT(context_var != NULL);
-    ASSERT(catch_block_ != NULL || finally_block_ != NULL);
+    ASSERT(catch_block_ != NULL);
   }
 
   SequenceNode* try_block() const { return try_block_; }
   CatchClauseNode* catch_block() const { return catch_block_; }
   SequenceNode* finally_block() const { return finally_block_; }
   const LocalVariable& context_var() const { return context_var_; }
   intptr_t try_index() const { return try_index_; }
 
   virtual void VisitChildren(AstNodeVisitor* visitor) const {
     try_block_->Visit(visitor);
@@ skipping 75 matching lines @@
   const intptr_t try_index_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(InlinedFinallyNode);
 };
 
 }  // namespace dart
 
 #undef DECLARE_COMMON_NODE_FUNCTIONS
 
 #endif  // VM_AST_H_