Handle nested position:sticky elements correctly (main thread)

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 2058 matching lines @@
         IntPoint centerPoint = roundedIntPoint(transformState.mappedPoint());
         transformState.move(toLayoutBox(container)->flipForWritingMode(
                                 LayoutPoint(centerPoint)) -
                             centerPoint);
       }
       mode &= ~ApplyContainerFlip;
     }
   }
 
   LayoutSize containerOffset = offsetFromContainer(container);
+
+  // TODO(smcgruer): This is inefficient. Instead we should avoid including
+  // offsetForInFlowPosition in offsetFromContainer when ignoring sticky.
+  if (isBoxModelObject() && isStickyPositioned() &&
+      (mode & IgnoreStickyOffset)) {

[flackr, 2017/02/24 01:33:33]

nit: Maybe do the mode check first since most of the time it will be false.

[smcgruer, 2017/02/24 14:17:43]

Done. Also removed the brackets to let it fit on one line; lmk if that's bad
style.

+    containerOffset -= toLayoutBoxModelObject(this)->offsetForInFlowPosition();
+  }
+
   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 1433 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