BR styled clear is ignored while partially relayouting.

Source/core/layout/LayoutBlockFlowLine.cpp

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2003, 2004, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All right reserved.
  * Copyright (C) 2010 Google 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
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 778 matching lines @@
 }
 
 void LayoutBlockFlow::layoutRunsAndFloatsInRange(LineLayoutState& layoutState,
     InlineBidiResolver& resolver, const InlineIterator& cleanLineStart,
     const BidiStatus& cleanLineBidiStatus)
 {
     const ComputedStyle& styleToUse = styleRef();
     bool paginated = view()->layoutState() && view()->layoutState()->isPaginated();
     LineMidpointState& lineMidpointState = resolver.midpointState();
     InlineIterator endOfLine = resolver.position();
-    bool checkForEndLineMatch = layoutState.endLine();
+    const bool needsToCheckEndLine = containsFloats() && lastChild() && lastChild()->isBR() && lastChild()->style()->clear();

[leviw_travelin_and_unemployed, 2015/04/24 18:55:47]

Driveby: This needs a better name. The addition of "needs" to the variable
doesn't make it clear what the difference between this and the bool below is.

Why are you checking lastChild directly? Does this only happen when the br in
question is the last child? That seems suspicious...

[changseok, 2015/04/24 21:53:08]

Yes it does as long as I know. If the br places in middle line of
LayoutBlockFlow and something visible like inlineBox or layoutBlock is followed,
then we can determine a endLine with the visible one. This bug only happens when
br with clear is the last child in LayoutBlockFlow. In this case, the end line
is the text node which is just before the last br and the start line is the
anchor. We calculate height with only those two lines so the height shrinks
after re-layout.
However we go over the two line and see the next line, br, we call clearFloats()
in the while loop and then we would finally have correct height of
layoutBlockFlow.

+    bool checkForEndLineMatch = layoutState.endLine() && !needsToCheckEndLine;
+
     LayoutTextInfo renderTextInfo;
     VerticalPositionCache verticalPositionCache;
 
     LineBreaker lineBreaker(this);
 
     while (!endOfLine.atEnd()) {
         bool logicalWidthIsAvailable = false;
 
         // FIXME: Is this check necessary before the first iteration or can it be moved to the end?
         if (checkForEndLineMatch) {
@@ skipping 1242 matching lines @@
     float logicalLeft = logicalLeftOffsetForLine(logicalHeight(), false).toFloat();
     float availableLogicalWidth = logicalRightOffsetForLine(logicalHeight(), false) - logicalLeft;
     updateLogicalWidthForAlignment(textAlign, 0, 0, logicalLeft, totalLogicalWidth, availableLogicalWidth, 0);
 
     if (!style()->isLeftToRightDirection())
         return logicalWidth() - logicalLeft;
     return logicalLeft;
 }
 
 }