[async-iteration] implement Async-from-Sync Iterator

src/builtins/builtins-async.h

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_BUILTINS_BUILTINS_ASYNC_H_
 #define V8_BUILTINS_BUILTINS_ASYNC_H_
 
 #include "src/builtins/builtins-promise.h"
 
 namespace v8 {
 namespace internal {
 
 class AsyncBuiltinsAssembler : public PromiseBuiltinsAssembler {
  public:
   explicit AsyncBuiltinsAssembler(CodeAssemblerState* state)
       : PromiseBuiltinsAssembler(state) {}
 
+  // Async Iterator

[neis, 2017/02/20 09:41:20]

I think you can drop this comment.

[caitp, 2017/02/20 17:09:34]

Done. I actually removed all changes to builtins-async.h since none of this
needs to be shared with the other users

+  Node* AllocateAsyncIteratorValueUnwrapContext(Node* native_context,
+                                                Node* done);
+
  protected:
   typedef std::function<Node*(Node*)> NodeGenerator1;
 
   // Perform steps to resume generator after `value` is resolved.
   // `on_reject_context_index` is an index into the Native Context, which should
   // point to a SharedFunctioninfo instance used to create the closure. The
   // value following the reject index should be a similar value for the resolve
   // closure. Returns the Promise-wrapped `value`.
   Node* Await(Node* context, Node* generator, Node* value, Node* outer_promise,
               const NodeGenerator1& create_closure_context,
               int on_resolve_context_index, int on_reject_context_index,
               bool is_predicted_as_caught);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_BUILTINS_BUILTINS_ASYNC_H_