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

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

Index: third_party/WebKit/Source/core/paint/PaintLayer.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayer.cpp b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
index 16f625873668c322d216058212ebb91e6e3d0ab5..0c895d1e5a4766d2ef1e6bf8df1342841085eb6c 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayer.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
@@ -838,6 +838,12 @@ void PaintLayer::UpdateLayerPosition() {
 
   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);