Don't always invalidate collapsed borders during table layout

third_party/WebKit/Source/core/layout/LayoutTableRow.cpp

 /*
  * Copyright (C) 1997 Martin Jones (mjones@kde.org)
  *           (C) 1997 Torben Weis (weis@kde.org)
  *           (C) 1998 Waldo Bastian (bastian@kde.org)
  *           (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2013
 *                Apple Inc.
  *               All rights reserved.
  *
@@ skipping 154 matching lines @@
   LayoutTableBoxComponent::AddChild(cell, before_child);
 
   // Generated content can result in us having a null section so make sure to
   // null check our parent.
   if (Parent()) {
     Section()->AddCell(cell, this);
     // When borders collapse, adding a cell can affect the the width of
     // neighboring cells.
     LayoutTable* enclosing_table = Table();
     if (enclosing_table && enclosing_table->CollapseBorders()) {
+      enclosing_table->InvalidateCollapsedBorders();

[wkorman, 2017/04/26 23:57:35]

Would we consider further optimizing this case? We invalidate the whole table
but we may only need to actually invalidate a portion of it.

Asking because, if the answer is perhaps down the line, then we should add a
TODO comment. If not, no worries.

[Xianzhu, 2017/04/27 15:43:40]

This marks the table's collapsed borders data structure dirty, and later we'll
update it. In next steps (https://codereview.chromium.org/2805103003/), update
of collapsed borders will be incremental with invalidation flag per cell, but
here we still need to invalidate the table collapsed borders here.

       if (LayoutTableCell* previous_cell = cell->PreviousCell())
         previous_cell->SetNeedsLayoutAndPrefWidthsRecalc(
             LayoutInvalidationReason::kTableChanged);
       if (LayoutTableCell* next_cell = cell->NextCell())
         next_cell->SetNeedsLayoutAndPrefWidthsRecalc(
             LayoutInvalidationReason::kTableChanged);
     }
   }
 
   if (before_child || NextRow())
@@ skipping 141 matching lines @@
   // won't fit but we avoid the complexity of that reading until it
   // is clarified. Tracked by crbug.com/675904
   if (RowIndex())
     return false;
   LayoutTableSection* header = Table()->Header();
   return header && Table()->SectionAbove(Section()) == header &&
          header->GetPaginationBreakability() != kAllowAnyBreaks;
 }
 
 }  // namespace blink