Avoid mutating frame owner when detaching a provisional frame.

third_party/WebKit/Source/core/html/HTMLFrameElementBase.h

Index: third_party/WebKit/Source/core/html/HTMLFrameElementBase.h
diff --git a/third_party/WebKit/Source/core/html/HTMLFrameElementBase.h b/third_party/WebKit/Source/core/html/HTMLFrameElementBase.h
index 2369fe5c8815455545c8da30cf7de35fdaf4f747..b4784525a02a63cabf43762d0000c2f2bd54d94b 100644
--- a/third_party/WebKit/Source/core/html/HTMLFrameElementBase.h
+++ b/third_party/WebKit/Source/core/html/HTMLFrameElementBase.h
@@ -34,9 +34,9 @@ class CORE_EXPORT HTMLFrameElementBase : public HTMLFrameOwnerElement {
   bool canContainRangeEndPoint() const final { return false; }
 
   // FrameOwner overrides:
-  ScrollbarMode scrollingMode() const override { return m_scrollingMode; }
-  int marginWidth() const override { return m_marginWidth; }
-  int marginHeight() const override { return m_marginHeight; }
+  ScrollbarMode scrollingMode() const final { return m_scrollingMode; }
+  int marginWidth() const final { return m_marginWidth; }
+  int marginHeight() const final { return m_marginHeight; }
 
  protected:
   HTMLFrameElementBase(const QualifiedName&, Document&);