Implement PaintLayer::scrollsWithViewport for SPv2.

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

Index: third_party/WebKit/Source/core/layout/LayoutBox.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutBox.cpp b/third_party/WebKit/Source/core/layout/LayoutBox.cpp
index fc48cab3e05c766569f25454af712a7460b27e11..39a850c55776e205b1f1aacccab4d97e0f0a83e0 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBox.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutBox.cpp
@@ -673,10 +673,10 @@ void LayoutBox::scrollRectToVisible(const LayoutRect& rect,
     }
   }
 
-  // If we are fixed-position and scroll with the viewport, it is useless to
+  // If we are fixed-position and stick to the viewport, it is useless to
   // scroll the parent.
-  if (style()->position() == FixedPosition && hasLayer() &&
-      layer()->scrollsWithViewport()) {
+  if (style()->position() == FixedPosition &&
+      containerForFixedPosition() == view()) {

[chrishtr, 2016/12/07 18:07:19]

This one was pretty easy to adjust to not call sticksToViewport, so I just
changed it. This method is called during layout, so it's not ok to update
all lifecycle phases.

     return;
   }
 
@@ -1027,7 +1027,7 @@ LayoutBox* LayoutBox::findAutoscrollable(LayoutObject* layoutObject) {
       !(layoutObject->isBox() && toLayoutBox(layoutObject)->canAutoscroll())) {
     // Do not start autoscroll when the node is inside a fixed-position element.
     if (layoutObject->isBox() && toLayoutBox(layoutObject)->hasLayer() &&
-        toLayoutBox(layoutObject)->layer()->scrollsWithViewport()) {
+        toLayoutBox(layoutObject)->layer()->sticksToViewport()) {
       return nullptr;
     }