Handle nested position:sticky elements

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

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2011 Apple Inc.
  *               All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved.
  *               (http://www.torchmobile.com/)
@@ skipping 2055 matching lines @@
         IntPoint centerPoint = roundedIntPoint(transformState.mappedPoint());
         transformState.move(toLayoutBox(container)->flipForWritingMode(
                                 LayoutPoint(centerPoint)) -
                             centerPoint);
       }
       mode &= ~ApplyContainerFlip;
     }
   }
 
   LayoutSize containerOffset = offsetFromContainer(container);
+  if (isBoxModelObject() && isStickyPositioned() && (mode & IgnoreSticky)) {
+    containerOffset -= toLayoutBoxModelObject(this)->offsetForInFlowPosition();

[flackr, 2017/01/31 18:33:00]

It is a little unfortunate to calculate this offset twice though, maybe leave a
TODO to not include it in the above call to offsetFromContainer?

[smcgruer, 2017/01/31 20:42:16]

Done.

+  }
+
   if (isLayoutFlowThread()) {
     // So far the point has been in flow thread coordinates (i.e. as if
     // everything in the fragmentation context lived in one tall single column).
     // Convert it to a visual point now, since we're about to escape the flow
     // thread.
     containerOffset += columnOffset(LayoutPoint(transformState.mappedPoint()));
   }
 
   // Text objects just copy their parent's computed style, so we need to ignore
   // them.
@@ skipping 1406 matching lines @@
     const blink::LayoutObject* root = object1;
     while (root->parent())
       root = root->parent();
     root->showLayoutTreeAndMark(object1, "*", object2, "-", 0);
   } else {
     WTFLogAlways("%s", "Cannot showLayoutTree. Root is (nil)");
   }
 }
 
 #endif