Create swapped-out opener RVHs after a process swap.

content/public/browser/site_instance.h

Index: content/public/browser/site_instance.h
diff --git a/content/public/browser/site_instance.h b/content/public/browser/site_instance.h
index 66081ec1f1f53feb38bf64a5fc5d4cb61c24fb33..d68989e9df5863d2c9e9ab35e4e260ebc1ead545 100644
--- a/content/public/browser/site_instance.h
+++ b/content/public/browser/site_instance.h
@@ -82,6 +82,11 @@ class CONTENT_EXPORT SiteInstance : public base::RefCounted<SiteInstance> {
   // Darin suggests.
   virtual SiteInstance* GetRelatedSiteInstance(const GURL& url) = 0;
 
+  // Returns whether the given SiteInstance is in the same BrowsingInstance as
+  // this one.  If so, JavaScript interactions that are permitted across
+  // origins (e.g., postMessage) should be supported.
+  virtual bool IsRelatedSiteInstance(const SiteInstance* instance) = 0;
+
   // Factory method to create a new SiteInstance.  This will create a new
   // new BrowsingInstance, so it should only be used when creating a new tab
   // from scratch (or similar circumstances).  Callers should ensure that