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 fc8c264fbee6d8a73b0470a6766aaa0ee381cb52..57cb3c3b1db718276190884cece9fb254306d1d3 100644
--- a/third_party/WebKit/Source/core/inspector/InspectorDOMAgent.h
+++ b/third_party/WebKit/Source/core/inspector/InspectorDOMAgent.h
@@ -109,6 +109,7 @@ public:
     void enable(ErrorString*) override;
     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, std::unique_ptr<protocol::Array<String>>* classNames) override;
     void requestChildNodes(ErrorString*, int nodeId, const Maybe<int>& depth) override;
     void querySelector(ErrorString*, int nodeId, const String& selector, int* outNodeId) override;
@@ -235,6 +236,8 @@ private:
 
     Member<InspectorRevalidateDOMTask> revalidateTask();
 
+    void visitLayoutTreeNodes(Node*, protocol::Array<protocol::DOM::LayoutTreeNode>&);
+
     v8::Isolate* m_isolate;
     Member<InspectedFrames> m_inspectedFrames;
     v8_inspector::V8InspectorSession* m_v8Session;