Why this CL triggers an OilPan crash.

third_party/WebKit/Source/core/page/Page.h

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2013 Apple Inc. All rights
  * reserved.
  * Copyright (C) 2008 Torch Mobile Inc. All rights reserved.
  * (http://www.torchmobile.com/)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 89 matching lines @@
     Member<ChromeClient> chrome_client;
     ContextMenuClient* context_menu_client;
     EditorClient* editor_client;
     SpellCheckerClient* spell_checker_client;
   };
 
   static Page* Create(PageClients& page_clients) {
     return new Page(page_clients);
   }
 
+  // Special value that can be passed as |browsing_instance_id| argument to
+  // CreateOrdinary method.  This value designates a page that should not be
+  // related to any other page (example of such a page would be a print-preview
+  // page that adds print header and footer on top of a real page).
+  static const int kUnknownBrowsingInstance = -1;
+
   // An "ordinary" page is a fully-featured page owned by a web view.
-  static Page* CreateOrdinary(PageClients&);
+  static Page* CreateOrdinary(PageClients&, int browsing_instance_id);
 
   ~Page() override;
 
   void CloseSoon();
   bool IsClosing() const { return is_closing_; }
 
   using PageSet = PersistentHeapHashSet<WeakMember<Page>>;
 
   // Return the current set of full-fledged, ordinary pages.
   // Each created and owned by a WebView.
   //
   // This set does not include Pages created for other, internal purposes
   // (SVGImages, inspector overlays, page popups etc.)
   static PageSet& OrdinaryPages();
 
+  // Returns a set of pages related to the current browsing context.  See also
+  // https://html.spec.whatwg.org/multipage/browsers.html#unit-of-related-browsing-contexts
+  const PageSet& RelatedPages();
+
   static void PlatformColorsChanged();
 
   void SetNeedsRecalcStyleInAllFrames();
   void UpdateAcceleratedCompositingSettings();
 
   ViewportDescription GetViewportDescription() const;
 
   static void RefreshPlugins();
   PluginData* GetPluginData(SecurityOrigin* main_frame_origin) const;
 
@@ skipping 212 matching lines @@
 
   PageVisibilityState visibility_state_;
 
   bool is_cursor_visible_;
 
 #if DCHECK_IS_ON()
   bool is_painting_ = false;
 #endif
 
   int subframe_count_;
+
+  int browsing_instance_id_ = kUnknownBrowsingInstance;
 };
 
 extern template class CORE_EXTERN_TEMPLATE_EXPORT Supplement<Page>;
 
 }  // namespace blink
 
 #endif  // Page_h