[cc] Change semantics of fixed-pos container layer

third_party/WebKit/Source/core/frame/VisualViewport.cpp

Index: third_party/WebKit/Source/core/frame/VisualViewport.cpp
diff --git a/third_party/WebKit/Source/core/frame/VisualViewport.cpp b/third_party/WebKit/Source/core/frame/VisualViewport.cpp
index fd7477384c459eb4efef22a624703aca9a7bfa1b..4ac727db691321605992f3ccb867c2d900f2a77d 100644
--- a/third_party/WebKit/Source/core/frame/VisualViewport.cpp
+++ b/third_party/WebKit/Source/core/frame/VisualViewport.cpp
@@ -347,10 +347,12 @@ void VisualViewport::CreateLayerTree() {
   overlay_scrollbar_horizontal_ = GraphicsLayer::Create(this);
   overlay_scrollbar_vertical_ = GraphicsLayer::Create(this);
 
+  // What is it really for? Are there any fixed-pos layers positioned
+  // by the VisualViewport actually?

[bokan, 2017/04/26 21:17:56]

I believe this was a temporary state meant only to support running in either
modes that never got removed. IMO, we can probably get rid of this, I think only
the outer viewport container layer (the PLC's container layer) should be a
ContainerForFixedPositionLayers.

[trchen, 2017/05/01 21:24:13]

I removed it in patch set 2, but on a second thought, I think we'd better change
on thing at a time so added it back.

   ScrollingCoordinator* coordinator = GetPage().GetScrollingCoordinator();
   DCHECK(coordinator);
   coordinator->SetLayerIsContainerForFixedPositionLayers(
-      inner_viewport_scroll_layer_.get(), true);
+      page_scale_layer_.get(), true);
 
   // Set masks to bounds so the compositor doesn't clobber a manually
   // set inner viewport container layer size.