Implement FullScreen using top layer.

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

Index: third_party/WebKit/Source/core/layout/LayoutBox.h
diff --git a/third_party/WebKit/Source/core/layout/LayoutBox.h b/third_party/WebKit/Source/core/layout/LayoutBox.h
index 7bdeb24e54af108bb8041020485bb065e810cb8e..b5fffef359ad12619e313d8066798e7c2d39e653 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBox.h
+++ b/third_party/WebKit/Source/core/layout/LayoutBox.h
@@ -388,8 +388,8 @@ public:
 
     // IE extensions. Used to calculate offsetWidth/Height.  Overridden by inlines (LayoutFlow)
     // to return the remaining width on a given line (and the height of a single line).
-    LayoutUnit offsetWidth() const override { return m_frameRect.width(); }
-    LayoutUnit offsetHeight() const override { return m_frameRect.height(); }
+    LayoutUnit offsetWidth() const final { return m_frameRect.width(); }
+    LayoutUnit offsetHeight() const final { return m_frameRect.height(); }
 
     int pixelSnappedOffsetWidth() const final;
     int pixelSnappedOffsetHeight() const final;
@@ -728,8 +728,8 @@ public:
     LayoutUnit lineHeight(bool firstLine, LineDirectionMode, LinePositionMode = PositionOnContainingLine) const override;
     int baselinePosition(FontBaseline, bool firstLine, LineDirectionMode, LinePositionMode = PositionOnContainingLine) const override;
 
-    LayoutUnit offsetLeft() const override;
-    LayoutUnit offsetTop() const override;
+    LayoutUnit offsetLeft() const final;
+    LayoutUnit offsetTop() const final;
 
     LayoutPoint flipForWritingModeForChild(const LayoutBox* child, const LayoutPoint&) const;
     LayoutUnit flipForWritingMode(LayoutUnit position) const WARN_UNUSED_RETURN {