Move LayoutObject to satellite NodeLayoutData that hangs from a Node.

third_party/WebKit/Source/core/dom/Node.cpp

Index: third_party/WebKit/Source/core/dom/Node.cpp
diff --git a/third_party/WebKit/Source/core/dom/Node.cpp b/third_party/WebKit/Source/core/dom/Node.cpp
index b91538efcfaa7eb5ae14c5775966265e5ac000d0..bf2a5e12ca78cdb4aba7c2759446feab31b4bd62 100644
--- a/third_party/WebKit/Source/core/dom/Node.cpp
+++ b/third_party/WebKit/Source/core/dom/Node.cpp
@@ -310,10 +310,13 @@ NodeRareData& Node::EnsureRareData() {
   if (HasRareData())
     return *RareData();
 
-  if (IsElementNode())
-    data_.rare_data_ = ElementRareData::Create(data_.layout_object_);
-  else
-    data_.rare_data_ = NodeRareData::Create(data_.layout_object_);
+  if (IsElementNode()) {
+    data_.rare_data_ =
+        ElementRareData::Create(data_.layout_data_->GetLayoutObject());

[esprehn, 2017/04/10 22:20:12]

You need to store the layout_data_ inside the ElementRareData, not the
LayoutObject, otherwise the union doesn't work. Also this would crash when
layout_data_ is null.

This should be ElementRareData::Create(data_.layout_data_)

and you need some kind of EnsureLayoutData(), I also think we want to avoid any
new branches, which means we need to use some kind of shared empty LayoutData
instance to Node::layoutObject() doesn't need another branch, and
setLayoutObject() (or any setter) checks if Node::layout_data_ ==
NodeLayoutData::sharedEmptyData() and allocates a non shared one if it is.

[nainar, 2017/04/11 01:16:20]

Referring back to IRL conversation. We shouldn't store the LayoutObject on
RareData anymore and just on NodeLayoutData. 

[nainar, 2017/04/13 00:10:22]

NodeRareDataBase and its descendants now store NodeLayoutData.

Added the static empty_shared_data instance of NodeLayoutData

+  } else {
+    data_.rare_data_ =
+        NodeRareData::Create(data_.layout_data_->GetLayoutObject());
+  }
 
   DCHECK(data_.rare_data_);
   SetFlag(kHasRareDataFlag);