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 1545 matching lines @@
         // the replaced elements later. In partial layout mode, line boxes are not
         // deleted and only dirtied. In that case, we can layout the replaced
         // elements at the same time.
         Vector<LayoutBox*> replacedChildren;
         for (InlineWalker walker(this); !walker.atEnd(); walker.advance()) {
             LayoutObject* o = walker.current();
 
             if (!layoutState.hasInlineChild() && o->isInline())
                 layoutState.setHasInlineChild(true);
 
+            if (o->isBR() && o->style()->clear() != CNONE)
+                layoutState.setContainsBRWithClear(true);
+
             if (o->isReplaced() || o->isFloating() || o->isOutOfFlowPositioned()) {
                 LayoutBox* box = toLayoutBox(o);
 
                 updateBlockChildDirtyBitsBeforeLayout(relayoutChildren, *box);
 
                 if (o->isOutOfFlowPositioned()) {
                     o->containingBlock()->insertPositionedObject(box);
                 } else if (o->isFloating()) {
                     layoutState.floats().append(FloatWithRect(box));
                 } else if (isFullLayout || o->needsLayout()) {
@@ skipping 275 matching lines @@
     }
 
     return true;
 }
 
 bool LayoutBlockFlow::matchedEndLine(LineLayoutState& layoutState, const InlineBidiResolver& resolver, const InlineIterator& endLineStart, const BidiStatus& endLineStatus)
 {
     if (resolver.position() == endLineStart) {
         if (resolver.status() != endLineStatus)
             return false;
+
+        // For partial layout where the block contains floats, the end line here is the last visible one.
+        // It misleads shorter height of the block than expected. We should check until the end line

[leviw_travelin_and_unemployed, 2015/05/20 21:22:29]

"It misleads shorter height of the block than expected" doesn't make sense :-/

[changseok, 2015/05/21 09:32:40]

Hrm.. what does not make sense to you? If you could point it out a little bit
more in depth, it would be much helpful.

Not sure of your thought though.. then how about this?
"For partial layout where the block contains floats, the end line here is the
last visible one. Due to calculating only these visible lines for the block
height, invisible br having clear style is ignored so that it causes shorter
height of the block than expected. We should check until the end line of the
block for the case."

[leviw_travelin_and_unemployed, 2015/05/21 17:49:50]

It's not proper English... "shorter height of the block" is not a sensible
direct object for misleads...
Last visible float?
What do you mean "visible" here?

I think what you're trying to say is that a trailing BR can be collapsed as it
usually doesn't contribute to the height, but if it has a clear style we need to
force it to layout in the context of floats to honor that style.

[changseok, 2015/05/22 08:47:35]

Oops, English is not my mother language so I used to make this kind of errors.
Sorry about that. :P
I meant last visible line.
What I meant for visible was something to have actual contents so it takes a
visual region. For example, empty span, <span></span> is not visible, but
<span>text</span> is visible.
Yeah. same context, but your summary is neater. May I just use yours?

+        // of the block for the case.
+        if (layoutState.containsBRWithClear() && containsFloats())
+            return false;
         return checkPaginationAndFloatsAtEndLine(layoutState);
     }
 
     // The first clean line doesn't match, but we can check a handful of following lines to try
     // to match back up.
     static int numLines = 8; // The # of lines we're willing to match against.
     RootInlineBox* originalEndLine = layoutState.endLine();
     RootInlineBox* line = originalEndLine;
     for (int i = 0; i < numLines && line; i++, line = line->nextRootBox()) {
         if (line->lineBreakObj() == resolver.position().object() && line->lineBreakPos() == resolver.position().offset()) {
@@ skipping 180 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;
 }
 
 }