Add a DOM.getLayoutTreeNodes devtools command

third_party/WebKit/Source/core/inspector/InspectorDOMAgent.h

Index: third_party/WebKit/Source/core/inspector/InspectorDOMAgent.h
diff --git a/third_party/WebKit/Source/core/inspector/InspectorDOMAgent.h b/third_party/WebKit/Source/core/inspector/InspectorDOMAgent.h
index 46972ca875958a62bee88df2eae67a9678011990..32d10c0905cae9a7315a639d715a71d2d1bd0889 100644
--- a/third_party/WebKit/Source/core/inspector/InspectorDOMAgent.h
+++ b/third_party/WebKit/Source/core/inspector/InspectorDOMAgent.h
@@ -122,6 +122,10 @@ class CORE_EXPORT InspectorDOMAgent final
   void disable(ErrorString*) override;
   void getDocument(ErrorString*,
                    std::unique_ptr<protocol::DOM::Node>* root) override;
+  void getLayoutTreeNodes(
+      ErrorString*,
+      std::unique_ptr<protocol::Array<protocol::DOM::LayoutTreeNode>>*
+          layoutTreeNodes) override;
   void collectClassNamesFromSubtree(
       ErrorString*,
       int nodeId,
@@ -351,6 +355,9 @@ class CORE_EXPORT InspectorDOMAgent final
 
   Member<InspectorRevalidateDOMTask> revalidateTask();
 
+  void visitLayoutTreeNodes(Node*,
+                            protocol::Array<protocol::DOM::LayoutTreeNode>&);
+
   v8::Isolate* m_isolate;
   Member<InspectedFrames> m_inspectedFrames;
   v8_inspector::V8InspectorSession* m_v8Session;