NOT FOR REVIEW - Update comp-scrolling state at a well defined point in the pipeline.

Source/core/page/FrameView.cpp

Index: Source/core/page/FrameView.cpp
diff --git a/Source/core/page/FrameView.cpp b/Source/core/page/FrameView.cpp
index 636768f8a632285da6f063abaec6d3ccd8b1fba6..08f931278066b91181e1435c2fb0493c0333fe03 100644
--- a/Source/core/page/FrameView.cpp
+++ b/Source/core/page/FrameView.cpp
@@ -710,6 +710,10 @@ void FrameView::updateCompositingLayersAfterStyleChange()
     if (!renderView)
         return;
 
+    // PATCH 2
+    // Catch promotions due to style changes (e.g., z-order changes).
+    renderView->compositor()->updateCompositingRequirementsState(CompositingUpdateAfterStyleChange);
+
     // If we expect to update compositing after an incipient layout, don't do so here.
     if (m_doingPreLayoutStyleUpdate || layoutPending() || renderView->needsLayout())
         return;
@@ -727,6 +731,9 @@ void FrameView::updateCompositingLayersAfterLayout()
 
     // This call will make sure the cached hasAcceleratedCompositing is updated from the pref
     renderView->compositor()->cacheAcceleratedCompositingFlags();
+    // PATCH 2
+    // Catch promotions due to layout changes (e.g., content now overflows).
+    renderView->compositor()->updateCompositingRequirementsState(CompositingUpdateAfterLayout);
     renderView->compositor()->updateCompositingLayers(CompositingUpdateAfterLayout);
 }