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

third_party/WebKit/Source/core/inspector/InspectorCSSAgent.cpp

 /*
  * Copyright (C) 2010, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1.  Redistributions of source code must retain the above copyright
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  *     notice, this list of conditions and the following disclaimer in the
@@ skipping 2284 matching lines @@
           text_bounds, owner_element->GetDocument(), nullptr, colors);
     }
   }
 
   *result = protocol::Array<String>::create();
   for (auto color : colors)
     result->fromJust()->addItem(color.SerializedAsCSSComponentValue());
   return Response::OK();
 }
 
 Response InspectorCSSAgent::getLayoutTreeAndStyles(

[pfeldman, 2017/05/15 18:42:18]

Do we still need it?

[Eric Seckler, 2017/05/17 10:44:31]

Not really. I was going to remove it and move the implementation to the
DOMSnapshotAgent if feasible, but only after we update headless clients
including the FlatDomTreeExtractor to stop using this.

We can do this in this patch, too, once we agree on the approach here :)

     std::unique_ptr<protocol::Array<String>> style_whitelist,
     std::unique_ptr<protocol::Array<protocol::CSS::LayoutTreeNode>>*
         layout_tree_nodes,
     std::unique_ptr<protocol::Array<protocol::CSS::ComputedStyle>>*
         computed_styles) {
-  dom_agent_->GetDocument()->UpdateStyleAndLayoutTree();
+  Document* document = dom_agent_->GetDocument();
+  if (!document)
+    return Response::Error("Document is not available");
+
+  document->UpdateStyleAndLayoutTree();
 
   // Look up the CSSPropertyIDs for each entry in |styleWhitelist|.
   Vector<std::pair<String, CSSPropertyID>> css_property_whitelist;
   for (size_t i = 0; i < style_whitelist->length(); i++) {
     CSSPropertyID property_id = cssPropertyID(style_whitelist->get(i));
     if (property_id == CSSPropertyInvalid)
       continue;
     css_property_whitelist.push_back(
         std::make_pair(style_whitelist->get(i), property_id));
   }
@@ skipping 214 matching lines @@
   visitor->Trace(css_style_sheet_to_inspector_style_sheet_);
   visitor->Trace(document_to_css_style_sheets_);
   visitor->Trace(invalidated_documents_);
   visitor->Trace(node_to_inspector_style_sheet_);
   visitor->Trace(inspector_user_agent_style_sheet_);
   visitor->Trace(tracker_);
   InspectorBaseAgent::Trace(visitor);
 }
 
 }  // namespace blink