Remove unnecessary anonymous blocks when splitting anonymous boxes

third_party/WebKit/Source/core/layout/LayoutBox.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. 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
@@ skipping 4354 matching lines @@
         // Because we may have added some sections with already computed column structures, we need to
         // sync the table structure with them now. This avoids crashes when adding new cells to the table.
         toLayoutTable(box)->forceSectionsRecalc();
     } else if (box->isTableSection()) {
         toLayoutTableSection(box)->setNeedsCellRecalc();
     }
 
     box->setNeedsLayoutAndPrefWidthsRecalcAndFullPaintInvalidation(LayoutInvalidationReason::AnonymousBlockChange);
 }
 
+static void collapseLoneAnonymousBlockChild(LayoutObject* child)
+{
+    ASSERT(child);
+    if (!child->isAnonymousBlock())
+        return;
+    LayoutObject* parent = child->parent();
+    if (!parent->isLayoutBlock())
+        return;
+    LayoutBlock::collapseAnonymousBlockChild(toLayoutBlock(parent), toLayoutBlock(child));
+}
+
 LayoutObject* LayoutBox::splitAnonymousBoxesAroundChild(LayoutObject* beforeChild)
 {
     bool didSplitParentAnonymousBoxes = false;
 
     while (beforeChild->parent() != this) {
         LayoutBox* boxToSplit = toLayoutBox(beforeChild->parent());
         if (boxToSplit->slowFirstChild() != beforeChild && boxToSplit->isAnonymous()) {
             didSplitParentAnonymousBoxes = true;
 
             // We have to split the parent box into two boxes and move children
             // from |beforeChild| to end into the new post box.
             LayoutBox* postBox = boxToSplit->createAnonymousBoxWithSameTypeAs(this);
             postBox->setChildrenInline(boxToSplit->childrenInline());
             LayoutBox* parentBox = toLayoutBox(boxToSplit->parent());
             // We need to invalidate the |parentBox| before inserting the new node
             // so that the table paint invalidation logic knows the structure is dirty.
             // See for example LayoutTableCell:clippedOverflowRectForPaintInvalidation.
             markBoxForRelayoutAfterSplit(parentBox);
             parentBox->virtualChildren()->insertChildNode(parentBox, postBox, boxToSplit->nextSibling());
             boxToSplit->moveChildrenTo(postBox, beforeChild, 0, true);
 
+            LayoutObject* child = postBox->slowFirstChild();
+            if (child && !child->nextSibling())
+                collapseLoneAnonymousBlockChild(child);
+            child = boxToSplit->slowFirstChild();

[mstensho (USE GERRIT), 2016/02/01 12:25:36]

Could ASSERT(child) here (and above) instead of "if (child)". Why split if there
are no children?

[rhogan, 2016/02/02 21:38:25]

True. I think we should ASSERT and null check though. 

+            if (child && !child->previousSibling())
+                collapseLoneAnonymousBlockChild(child);
+
             markBoxForRelayoutAfterSplit(boxToSplit);
             markBoxForRelayoutAfterSplit(postBox);
 
             beforeChild = postBox;
         } else {
             beforeChild = boxToSplit;
         }
     }
 
     if (didSplitParentAnonymousBoxes)
@@ skipping 227 matching lines @@
 
 void LayoutBox::clearPercentHeightDescendants()
 {
     for (LayoutObject* curr = slowFirstChild(); curr; curr = curr->nextInPreOrder(this)) {
         if (curr->isBox())
             toLayoutBox(curr)->removeFromPercentHeightContainer();
     }
 }
 
 } // namespace blink