RenderBlock::isSelfCollapsingBlock() should early exit on a relayout boundary

Source/core/rendering/RenderBlock.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) Research In Motion Limited 2010. All rights reserved.
  * Copyright (C) 2014 Samsung Electronics. 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 1160 matching lines @@
                 break;
             }
             setContinuation(0);
             destroy();
         }
     }
 }
 
 bool RenderBlock::isSelfCollapsingBlock() const
 {
-    // Placeholder elements are not laid out until the dimensions of their parent text control are known, so they
-    // don't get layout until their parent has had layout - this is unique in the layout tree and means
-    // when we call isSelfCollapsingBlock on them we find that they still need layout.
-    ASSERT(!needsLayout() || (node() && node()->isElementNode() && toElement(node())->shadowPseudoId() == "-webkit-input-placeholder"));
-
     // We are not self-collapsing if we
     // (a) have a non-zero height according to layout (an optimization to avoid wasting time)
     // (b) are a table,
     // (c) have border/padding,
     // (d) have a min-height
     // (e) have specified that one of our margins can't collapse using a CSS extension
     // (f) establish a new block formatting context.
 
+    // The early exit must be done before we check for clean layout.
+    // We should be able to give a quick answer if the box is a relayout boundary.
+    // Being a relayout boundary implies a block formatting context, and also

[ojan, 2014/04/24 17:22:09]

This comment is a little confusing. It talks about relayout boundaries, but the
code is only checking block formatting context. 

+    // our internal layout shouldn't affect our container in any way.
     if (createsBlockFormattingContext())
         return false;
 
+    // Placeholder elements are not laid out until the dimensions of their parent text control are known, so they
+    // don't get layout until their parent has had layout - this is unique in the layout tree and means
+    // when we call isSelfCollapsingBlock on them we find that they still need layout.
+    ASSERT(!needsLayout() || (node() && node()->isElementNode() && toElement(node())->shadowPseudoId() == "-webkit-input-placeholder"));
+
     if (logicalHeight() > 0
         || isTable() || borderAndPaddingLogicalHeight()
         || style()->logicalMinHeight().isPositive()
         || style()->marginBeforeCollapse() == MSEPARATE || style()->marginAfterCollapse() == MSEPARATE)
         return false;
 
     Length logicalHeightLength = style()->logicalHeight();
     bool hasAutoHeight = logicalHeightLength.isAuto();
     if (logicalHeightLength.isPercent() && !document().inQuirksMode()) {
         hasAutoHeight = true;
@@ skipping 3791 matching lines @@
 void RenderBlock::showLineTreeAndMark(const InlineBox* markedBox1, const char* markedLabel1, const InlineBox* markedBox2, const char* markedLabel2, const RenderObject* obj) const
 {
     showRenderObject();
     for (const RootInlineBox* root = firstRootBox(); root; root = root->nextRootBox())
         root->showLineTreeAndMark(markedBox1, markedLabel1, markedBox2, markedLabel2, obj, 1);
 }
 
 #endif
 
 } // namespace WebCore