Initial touch-action main thread implementation

Source/core/dom/Node.h

Index: Source/core/dom/Node.h
diff --git a/Source/core/dom/Node.h b/Source/core/dom/Node.h
index a139faf87244edc40489ab7439e8dca63ccf213c..d707997969eab235b2b96bfc5bf4f39b7710123e 100644
--- a/Source/core/dom/Node.h
+++ b/Source/core/dom/Node.h
@@ -525,6 +525,7 @@ public:
     // Integration with rendering tree
 
     // As renderer() includes a branch you should avoid calling it repeatedly in hot code paths.
+    // Note that if a Node has a renderer, it's parentNode is guaranteed to have one as well.
     RenderObject* renderer() const { return hasRareData() ? m_data.m_rareData->renderer() : m_data.m_renderer; };
     void setRenderer(RenderObject* renderer)
     {