Enable position:sticky for <thead> and <tr> elements

third_party/WebKit/Source/core/css/resolver/StyleAdjuster.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 2004-2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2006, 2007 Nicholas Shanks (webkit@nickshanks.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple Inc.
  * All rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007, 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved.
  * (http://www.torchmobile.com/)
@@ skipping 322 matching lines @@
   if (style.display() == EDisplay::kContents)
     return;
 
   // FIXME: Don't support this mutation for pseudo styles like first-letter or
   // first-line, since it's not completely clear how that should work.
   if (style.display() == EDisplay::kInline &&
       style.styleType() == PseudoIdNone &&
       style.getWritingMode() != layoutParentStyle.getWritingMode())
     style.setDisplay(EDisplay::kInlineBlock);
 
-  // We do not honor position: relative or sticky for table rows, headers, and
-  // footers. This is correct for position: relative in CSS2.1 (and caused a
-  // crash in containingBlock() on some sites) and position: sticky is defined
-  // as following position: relative behavior for table elements. It is
-  // incorrect for CSS3.
+  // We do not honor position: relative for table rows, headers, and footers.
+  // This is correct for CSS2.1 (and honoring it caused a crash in
+  // containingBlock() on some sites). It is incorrect for CSS3.
   if ((style.display() == EDisplay::kTableHeaderGroup ||
        style.display() == EDisplay::kTableRowGroup ||
        style.display() == EDisplay::kTableFooterGroup ||
        style.display() == EDisplay::kTableRow) &&
-      style.hasInFlowPosition())
+      style.position() == EPosition::kRelative)

[mstensho (USE GERRIT), 2017/03/29 18:27:55]

This change will let e.g. a table-row act as a containing block for absolutely
positioned descendants. I cannot imagine that it will work out of the box.

<div style="display:table-row; position:sticky;">
    <div style="position:absolute;"></div>
</div>

     style.setPosition(EPosition::kStatic);
 
   // Cannot support position: sticky for table columns and column groups because
   // current code is only doing background painting through columns / column
   // groups.
   if ((style.display() == EDisplay::kTableColumnGroup ||
        style.display() == EDisplay::kTableColumn) &&
       style.position() == EPosition::kSticky)
     style.setPosition(EPosition::kStatic);
 
@@ skipping 143 matching lines @@
       style.setDisplay(EDisplay::kBlock);
 
     // Columns don't apply to svg text elements.
     if (isSVGTextElement(*element))
       style.clearMultiCol();
   }
   adjustStyleForAlignment(style, layoutParentStyle);
 }
 
 }  // namespace blink