Have the unload event execute in background on cross-site navigations

content/browser/frame_host/frame_tree.h

Index: content/browser/frame_host/frame_tree.h
diff --git a/content/browser/frame_host/frame_tree.h b/content/browser/frame_host/frame_tree.h
index 8aa85bb0e72db66510e729eff46e479212bc2d15..f536a2d97d033ae0103156d9822c91d6698b8e13 100644
--- a/content/browser/frame_host/frame_tree.h
+++ b/content/browser/frame_host/frame_tree.h
@@ -130,8 +130,8 @@ class CONTENT_EXPORT FrameTree {
   FrameTreeNode* FindByFrameID(int64 frame_id);
 
  private:
-  typedef std::pair<RenderViewHostImpl*, int> RenderViewHostRefCount;
-  typedef base::hash_map<int, RenderViewHostRefCount> RenderViewHostMap;
+  typedef base::hash_map<int, RenderViewHostImpl*> RenderViewHostMap;
+  typedef std::multimap<int, RenderViewHostImpl*> RenderViewHostMultiMap;
 
   // These delegates are installed into all the RenderViewHosts and
   // RenderFrameHosts that we create.
@@ -140,15 +140,18 @@ class CONTENT_EXPORT FrameTree {
   RenderWidgetHostDelegate* render_widget_delegate_;
   RenderFrameHostManager::Delegate* manager_delegate_;
 
-  // Map of SiteInstance ID to a (RenderViewHost, refcount) pair.  This allows
-  // us to look up the RenderViewHost for a given SiteInstance when creating
-  // RenderFrameHosts, and it allows us to call Shutdown on the RenderViewHost
-  // and remove it from the map when no more RenderFrameHosts are using it.
+  // Map of SiteInstance ID to a RenderViewHost.  This allows us to look up the
+  // RenderViewHost for a given SiteInstance when creating RenderFrameHosts, and
+  // it allows us to call Shutdown on the RenderViewHost and remove it from the
+  // map when no more RenderFrameHosts are using it.
   //
   // Must be declared before |root_| so that it is deleted afterward.  Otherwise
   // the map will be cleared before we delete the RenderFrameHosts in the tree.
   RenderViewHostMap render_view_host_map_;
 
+  // Map of SiteInstance ID to RenderViewHosts that are pending shutdown.
+  RenderViewHostMultiMap render_view_host_pending_shutdown_map_;

[nasko, 2014/01/23 23:34:58]

Why is this a multimap? There should be only one RVH per SiteInstance in a
FrameTree.

[clamy, 2014/01/24 17:01:54]

It seems that we can end up reusing the same site instanec id at least, which
can cause us to have at least one active RVH and one RVH pending shutdown for
the same site instance id (that happens in one of the browser tests). Therefore,
I was worried about corner cases where we would navigate fast enough so that we
end up with two RVH pending shutdown and sharing the same site instance id.

+
   scoped_ptr<FrameTreeNode> root_;
 
   base::Callback<void(RenderViewHostImpl*, int64)> on_frame_removed_;