Set ComputedStyle on Node and use that in buildOwnLayout()

third_party/WebKit/Source/core/dom/NodeComputedStyle.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2008 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
@@ skipping 40 matching lines @@
     if (isHTMLOptGroupElement(*this) || isHTMLOptionElement(this))
         return nonLayoutObjectComputedStyle();
     if (hasRareData()) {
         NodeRareData* rareData = this->rareData();
         DCHECK(rareData->isElementRareData());
         return static_cast<ElementRareData*>(rareData)->ensureComputedStyle();
     }
     return m_data.m_computedStyle;
 }
 
+inline void Node::setComputedStyle(PassRefPtr<ComputedStyle> computedStyle)
+{
+    if (hasRareData()) {

[sashab, 2016/07/06 04:22:02]

Is hasRareData() the check you want here? Maybe you want isElement().

Did you copy this code from somewhere or is this your own logic?

[nainar, 2016/07/06 04:51:53]

Yup. The ComputedStyle on Node can be stored in the following ways:

If the DataUnion is a NodeRareDataBase and has a LayoutObject - set the
ComputedStyle on that LayoutObject
If the DataUnion is an NodeRareDataBase (specifically an ElementRareData) - set
the ComputedStyle on that LayoutObject
If the DataUnion is a LayoutObject - set the ComputedStyle on that LayoutObject
If the DataUnion is a ComputedStyle - make it point to the new ComputedStyle
passed in. 

Bugs' had written up a draft of this code in his CL - however didn't land it as
it wasn't needed as part of that CL. I modified it a bit.

[sashab, 2016/07/06 05:10:40]

Could you re-write this as a single if-statement with 4 branches? Might be a
little easier to understand. Put what you've explained above in comments if you
can, in each branch. :)

+        if (hasLayoutObject()) {

[Bugs Nash, 2016/07/06 04:30:42]

this isn't necessary

[nainar, 2016/07/06 04:51:53]

Agreed in a screen-to-screen conversation that:

Quoting the design doc here: "If NodeRareDataBase exists, the ComputedStyle will
be stored within the LayoutObject, which is stored within the NodeRareDataBase
on the DataUnion. If there is no LayoutObject stored on NodeRareDataBase we
directly store the ComputedStyle on the NodeRareDataBase (specifically the
ElementRareData)."

+            m_data.m_rareData->layoutObject()->setStyleInternal(computedStyle);
+        } else {
+            NodeRareData* rareData = this->rareData();
+            DCHECK(rareData->isElementRareData());
+            static_cast<ElementRareData*>(rareData)->setComputedStyle(computedStyle);
+        }
+    } else {
+        if (hasLayoutObject()) {
+            m_data.m_layoutObject->setStyleInternal(computedStyle);
+        } else {
+            if (m_data.m_computedStyle)
+                m_data.m_computedStyle->deref();
+            m_data.m_computedStyle = computedStyle.leakRef();
+        }
+    }
+}
+
 inline const ComputedStyle* Node::parentComputedStyle() const
 {
     if (isSlotOrActiveInsertionPoint())
         return 0;
     ContainerNode* parent = LayoutTreeBuilderTraversal::parent(*this);
     return parent ? parent->computedStyle() : 0;
 }
 
 inline const ComputedStyle& Node::computedStyleRef() const
 {
     const ComputedStyle* style = computedStyle();
     DCHECK(style);
     return *style;
 }
 
 } // namespace blink
 #endif // NodeComputedStyle_h