Skip dirtying lines when attaching children prior to attaching oneself

third_party/WebKit/Source/core/layout/line/LineBoxList.cpp

 /*
  * Copyright (C) 2008 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 216 matching lines @@
 
     return false;
 }
 
 void LineBoxList::dirtyLinesFromChangedChild(LineLayoutItem container, LineLayoutItem child)
 {
     if (!container.parent() || (container.isLayoutBlock() && (container.selfNeedsLayout() || !container.isLayoutBlockFlow())))
         return;
 
     LineLayoutInline inlineContainer = container.isLayoutInline() ? LineLayoutInline(container) : LineLayoutInline();
+
+    // If we are attaching children dirtying lines is unnecessary as we will do a full layout
+    // of the inline's contents anyway.
+    if (inlineContainer && inlineContainer.node() && inlineContainer.node()->needsAttach())
+        return;
+
     InlineBox* firstBox = inlineContainer ? inlineContainer.firstLineBoxIncludingCulling() : firstLineBox();
 
     // If we have no first line box, then just bail early.
     if (!firstBox) {
         // For an empty inline, go ahead and propagate the check up to our parent, unless the parent
         // is already dirty.
         if (container.isInline() && !container.ancestorLineBoxDirty()) {
             container.parent().dirtyLinesFromChangedChild(container);
             container.setAncestorLineBoxDirty(); // Mark the container to avoid dirtying the same lines again across multiple destroy() calls of the same subtree.
         }
@@ skipping 71 matching lines @@
         ASSERT(child->prevLineBox() == prev);
         prev = child;
     }
     ASSERT(prev == m_lastLineBox);
 #endif
 }
 
 #endif
 
 } // namespace blink