[WIP] Migrate Fullscreen to use top layer instead of RenderFullScreen

Source/core/html/HTMLMediaElement.cpp

Index: Source/core/html/HTMLMediaElement.cpp
diff --git a/Source/core/html/HTMLMediaElement.cpp b/Source/core/html/HTMLMediaElement.cpp
index ed65abe872e271a83a47b550a83a90038999fd7f..424e866306f7e0b819e9384f89822f74a06fabb0 100644
--- a/Source/core/html/HTMLMediaElement.cpp
+++ b/Source/core/html/HTMLMediaElement.cpp
@@ -496,12 +496,18 @@ bool HTMLMediaElement::childShouldCreateRenderer(const NodeRenderingContext& chi
 {
     if (!hasMediaControls())
         return false;
+
     // <media> doesn't allow its content, including shadow subtree, to
     // be rendered. So this should return false for most of the children.
     // One exception is a shadow tree built for rendering controls which should be visible.
     // So we let them go here by comparing its subtree root with one of the controls.
-    return (mediaControls()->treeScope() == childContext.node()->treeScope()
-            && childContext.isOnUpperEncapsulationBoundary() && HTMLElement::childShouldCreateRenderer(childContext));
+    if ((mediaControls()->treeScope() == childContext.node()->treeScope()
+        && childContext.isOnUpperEncapsulationBoundary() && HTMLElement::childShouldCreateRenderer(childContext)))
+        return true;
+    if (childContext.node()->pseudoId() == BACKDROP)
+        return true;
+
+    return false;
 }
 
 Node::InsertionNotificationRequest HTMLMediaElement::insertedInto(ContainerNode* insertionPoint)