Only create sticky position constraints for constrained sticky position.

third_party/WebKit/Source/core/layout/compositing/CompositingInputsUpdater.cpp

Index: third_party/WebKit/Source/core/layout/compositing/CompositingInputsUpdater.cpp
diff --git a/third_party/WebKit/Source/core/layout/compositing/CompositingInputsUpdater.cpp b/third_party/WebKit/Source/core/layout/compositing/CompositingInputsUpdater.cpp
index 53d5dfb1acd5d8d7b2625c133039496d26ee4999..3b4e62297f3ea08908763c4f1925f3685fec791b 100644
--- a/third_party/WebKit/Source/core/layout/compositing/CompositingInputsUpdater.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/CompositingInputsUpdater.cpp
@@ -101,7 +101,7 @@ void CompositingInputsUpdater::updateRecursive(PaintLayer* layer,
   const PaintLayer* previousOverflowLayer = layer->ancestorOverflowLayer();
   layer->updateAncestorOverflowLayer(info.lastOverflowClipLayer);
   if (info.lastOverflowClipLayer && layer->needsCompositingInputsUpdate() &&
-      layer->layoutObject().style()->position() == EPosition::kSticky) {
+      layer->layoutObject().style()->hasStickyConstrainedPosition()) {

[chrishtr, 2017/03/27 16:28:07]

Which code clears out the sticky position constraints when it becomes
unconstrained?

[flackr, 2017/04/07 18:15:45]

LayoutBoxModelObject::styleDidChange checks if the style became constrained or
no longer constrained and in the latter case removes the constraints from the
layer.

     if (!RuntimeEnabledFeatures::rootLayerScrollingEnabled()) {
       if (info.lastOverflowClipLayer != previousOverflowLayer) {
         // Old ancestor scroller should no longer have these constraints.