Return the right top position for text selections when there are no previous root inline boxes.

Source/core/rendering/RootInlineBox.cpp

 /*
  * Copyright (C) 2003, 2006, 2008 Apple 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.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 385 matching lines @@
     return 0;
 }
 
 LayoutUnit RootInlineBox::selectionTop() const
 {
     LayoutUnit selectionTop = m_lineTop;
 
     if (m_hasAnnotationsBefore)
         selectionTop -= !renderer()->style()->isFlippedLinesWritingMode() ? computeOverAnnotationAdjustment(m_lineTop) : computeUnderAnnotationAdjustment(m_lineTop);
 
-    if (renderer()->style()->isFlippedLinesWritingMode())
+    if (renderer()->style()->isFlippedLinesWritingMode() || !prevRootBox())
         return selectionTop;
 
-    LayoutUnit prevBottom = prevRootBox() ? prevRootBox()->selectionBottom() : block()->borderBefore() + block()->paddingBefore();
+    LayoutUnit prevBottom = prevRootBox()->selectionBottom();
     if (prevBottom < selectionTop && block()->containsFloats()) {
         // This line has actually been moved further down, probably from a large line-height, but possibly because the
         // line was forced to clear floats.  If so, let's check the offsets, and only be willing to use the previous
         // line's bottom if the offsets are greater on both sides.
         LayoutUnit prevLeft = block()->logicalLeftOffsetForLine(prevBottom, false);
         LayoutUnit prevRight = block()->logicalRightOffsetForLine(prevBottom, false);
         LayoutUnit newLeft = block()->logicalLeftOffsetForLine(selectionTop, false);
         LayoutUnit newRight = block()->logicalRightOffsetForLine(selectionTop, false);
         if (prevLeft > newLeft || prevRight < newRight)
             return selectionTop;
@@ skipping 449 matching lines @@
 }
 
 #ifndef NDEBUG
 const char* RootInlineBox::boxName() const
 {
     return "RootInlineBox";
 }
 #endif
 
 } // namespace WebCore