Check BrowsingInstance before swapping prerenders.

content/public/browser/site_instance.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_PUBLIC_BROWSER_SITE_INSTANCE_H_
 #define CONTENT_PUBLIC_BROWSER_SITE_INSTANCE_H_
 
 #include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
 #include "content/common/content_export.h"
 #include "url/gurl.h"
 
 namespace content {
 class BrowserContext;
-class BrowsingInstance;
 class RenderProcessHost;
 
 ///////////////////////////////////////////////////////////////////////////////
 // SiteInstance interface.
 //
 // A SiteInstance represents a group of web pages that may be able to
 // synchronously script each other, and thus must live in the same renderer
 // process.
 //
 // We identify this group using a combination of where the page comes from
@@ skipping 74 matching lines @@
   // class from the rest of the codebase.)
   // TODO(creis): This may be an argument to build a pass_refptr<T> class, as
   // 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;
 
+  // Returns the total active WebContents count for this SiteInstance and all
+  // related SiteInstances in the same BrowsingInstance.
+  virtual size_t GetRelatedActiveContentsCount() const = 0;

[jam, 2014/04/30 16:13:23]

nit: remove the const, see
http://www.chromium.org/developers/content-module/content-api

[davidben, 2014/04/30 16:21:52]

Done.

+
   // 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
   // this SiteInstance becomes ref counted, by storing it in a scoped_refptr.
   //
   // The render process host factory may be NULL. See SiteInstance constructor.
   //
   // TODO(creis): This may be an argument to build a pass_refptr<T> class, as
   // Darin suggests.
   static SiteInstance* Create(content::BrowserContext* browser_context);
@@ skipping 22 matching lines @@
  protected:
   friend class base::RefCounted<SiteInstance>;
 
   SiteInstance() {}
   virtual ~SiteInstance() {}
 };
 
 }  // namespace content.
 
 #endif  // CONTENT_PUBLIC_BROWSER_SITE_INSTANCE_H_