[devtools] Add DOMSnapshot domain for dom+layout+style snapshots.

headless/public/util/flat_dom_tree_extractor.h

Index: headless/public/util/flat_dom_tree_extractor.h
diff --git a/headless/public/util/flat_dom_tree_extractor.h b/headless/public/util/flat_dom_tree_extractor.h
index 867c4594c75f646d175714bdcb7f2830394bbe3e..fdcc755f413362d5e4382ab10c3538ddcfcfdc0d 100644
--- a/headless/public/util/flat_dom_tree_extractor.h
+++ b/headless/public/util/flat_dom_tree_extractor.h
@@ -47,12 +47,8 @@ class HEADLESS_EXPORT FlatDomTreeExtractor {
    private:
     friend class FlatDomTreeExtractor;
 
-    // Owns the raw pointers in |dom_nodes_|.
-    std::unique_ptr<dom::GetFlattenedDocumentResult> document_result_;
-
-    // Owns the raw pointers in |layout_tree_nodes_|.
-    std::unique_ptr<css::GetLayoutTreeAndStylesResult>
-        layout_tree_and_styles_result_;
+    // Owns the raw pointers in |dom_nodes_| and |layout_tree_nodes_|.
+    std::unique_ptr<css::GetDocumentSnapshotResult> document_snapshot_result_;
 
     DISALLOW_COPY_AND_ASSIGN(DomTree);
   };
@@ -65,13 +61,9 @@ class HEADLESS_EXPORT FlatDomTreeExtractor {
                       DomResultCB callback);
 
  private:
-  void OnDocumentFetched(
-      std::unique_ptr<dom::GetFlattenedDocumentResult> result);
-
-  void OnLayoutTreeAndStylesFetched(
-      std::unique_ptr<css::GetLayoutTreeAndStylesResult> result);
+  void OnDocumentSnapshotResult(
+      std::unique_ptr<css::GetDocumentSnapshotResult> result);
 
-  void MaybeExtractDomTree();
   void EnumerateNodes(const dom::Node* node);
   void ExtractLayoutTreeNodes();
   void ExtractComputedStyles();