Adds a FlatDomTreeExtractor to headless

headless/public/util/dom_tree_extractor.h

 // Copyright 2016 The Chromium 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 HEADLESS_PUBLIC_UTIL_DOM_TREE_EXTRACTOR_H_
 #define HEADLESS_PUBLIC_UTIL_DOM_TREE_EXTRACTOR_H_
 
 #include <unordered_map>
 #include <vector>
 
 #include "base/macros.h"
 #include "headless/public/devtools/domains/css.h"
 #include "headless/public/devtools/domains/dom.h"
 
 namespace headless {
 class HeadlessDevToolsClient;
 
 // A utility class for extracting information from the DOM via DevTools. In
 // addition, it also extracts details of bounding boxes and layout text (NB the
 // exact layout should not be regarded as stable, it's subject to change without
 // notice).
+// TODO(alexclarke): Remove in favor of one using DOM.getFlattenedDocument.
 class DomTreeExtractor {
  public:
   explicit DomTreeExtractor(HeadlessDevToolsClient* devtools_client);
   ~DomTreeExtractor();
 
   using NodeId = int;
   using Index = size_t;
 
   class DomTree {
    public:
@@ skipping 47 matching lines @@
   bool work_in_progress_;
   HeadlessDevToolsClient* devtools_client_;  // NOT OWNED
   base::WeakPtrFactory<DomTreeExtractor> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(DomTreeExtractor);
 };
 
 }  // namespace headless
 
 #endif  // HEADLESS_PUBLIC_UTIL_DOM_TREE_EXTRACTOR_H_