Fix the bug that sticky element may not be correctly invalidated due to non-promotion

third_party/WebKit/Source/core/paint/PaintLayer.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights
  * reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
@@ skipping 820 matching lines @@
       // Adjust offset for absolute under in-flow positioned inline.
       LayoutSize offset =
           ToLayoutInline(containing_layer->GetLayoutObject())
               .OffsetForInFlowPositionedInline(ToLayoutBox(GetLayoutObject()));
       local_point += offset;
     }
   }
 
   if (GetLayoutObject().IsInFlowPositioned()) {
     LayoutSize new_offset = GetLayoutObject().OffsetForInFlowPosition();
+    if (GetLayoutObject().Style()->GetPosition() == EPosition::kSticky &&

[flackr, 2017/04/28 17:14:57]

Remove the check for position sticky, I don't think this needs to be special
cased. If we remove this check, does it fire if a position: relative; element
gets a new offset applied?

[yigu, 2017/04/28 20:01:29]

Done.

+        !HasCompositedLayerMapping() &&
+        OffsetForInFlowPosition() != new_offset) {
+      ObjectPaintInvalidator(GetLayoutObject())
+          .InvalidatePaintIncludingNonCompositingDescendants();
+    }
     if (rare_data_ || !new_offset.IsZero())
       EnsureRareData().offset_for_in_flow_position = new_offset;
     local_point.Move(new_offset);
   } else if (rare_data_) {
     rare_data_->offset_for_in_flow_position = LayoutSize();
   }
 
   location_ = local_point;
 
   if (scrollable_area_ && did_resize)
@@ skipping 2466 matching lines @@
 }
 
 void showLayerTree(const blink::LayoutObject* layoutObject) {
   if (!layoutObject) {
     LOG(INFO) << "Cannot showLayerTree. Root is (nil)";
     return;
   }
   showLayerTree(layoutObject->EnclosingLayer());
 }
 #endif