Why this CL triggers an OilPan crash.

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

Index: third_party/WebKit/Source/core/page/Page.h
diff --git a/third_party/WebKit/Source/core/page/Page.h b/third_party/WebKit/Source/core/page/Page.h
index e644faaeae13ee25d1b711e89c2bf3f8853501fc..128b34fcfafedd19c41480a5567c891ba0bd4f5d 100644
--- a/third_party/WebKit/Source/core/page/Page.h
+++ b/third_party/WebKit/Source/core/page/Page.h
@@ -107,8 +107,14 @@ class CORE_EXPORT Page final : public GarbageCollectedFinalized<Page>,
     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;
 
@@ -124,6 +130,10 @@ class CORE_EXPORT Page final : public GarbageCollectedFinalized<Page>,
   // (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();
@@ -356,6 +366,8 @@ class CORE_EXPORT Page final : public GarbageCollectedFinalized<Page>,
 #endif
 
   int subframe_count_;
+
+  int browsing_instance_id_ = kUnknownBrowsingInstance;
 };
 
 extern template class CORE_EXTERN_TEMPLATE_EXPORT Supplement<Page>;