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

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

Index: third_party/WebKit/Source/core/inspector/InspectorCSSAgent.cpp
diff --git a/third_party/WebKit/Source/core/inspector/InspectorCSSAgent.cpp b/third_party/WebKit/Source/core/inspector/InspectorCSSAgent.cpp
index e9bfe37f98c093e07819878b4e5a1bf6089d8b48..1169091ed338621218e597c7206daa0dc096b7eb 100644
--- a/third_party/WebKit/Source/core/inspector/InspectorCSSAgent.cpp
+++ b/third_party/WebKit/Source/core/inspector/InspectorCSSAgent.cpp
@@ -2302,13 +2302,30 @@ Response InspectorCSSAgent::getBackgroundColors(
   return Response::OK();
 }
 
-Response InspectorCSSAgent::getLayoutTreeAndStyles(
+Response InspectorCSSAgent::getDocumentSnapshot(
     std::unique_ptr<protocol::Array<String>> style_whitelist,
+    protocol::Maybe<int> dom_depth,
+    protocol::Maybe<bool> pierce,
+    std::unique_ptr<protocol::Array<protocol::DOM::Node>>* dom_nodes,
     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();
+  if (!dom_agent_->Enabled())
+    return Response::Error("DOM agent hasn't been enabled");
+
+  Document* document = dom_agent_->GetDocument();
+  if (!document)
+    return Response::Error("Document is not available");
+
+  // Update layout tree first, so that it won't change between
+  // getFlattenedDocument and VisitLayoutTreeNodes.
+  document->UpdateStyleAndLayoutTree();
+
+  Response response = dom_agent_->getFlattenedDocument(
+      std::move(dom_depth), std::move(pierce), dom_nodes);
+  if (!response.isSuccess())
+    return response;
 
   // Look up the CSSPropertyIDs for each entry in |styleWhitelist|.
   Vector<std::pair<String, CSSPropertyID>> css_property_whitelist;