[wip] Introduce SiteInstanceKeepAlive.

content/browser/frame_host/render_frame_host_manager.h

Index: content/browser/frame_host/render_frame_host_manager.h
diff --git a/content/browser/frame_host/render_frame_host_manager.h b/content/browser/frame_host/render_frame_host_manager.h
index 5e23c581e9880038071f2b8e5f124ac3e53553ea..bdb490a6fcac4b37d248b1ce8c392a69e9f89dc8 100644
--- a/content/browser/frame_host/render_frame_host_manager.h
+++ b/content/browser/frame_host/render_frame_host_manager.h
@@ -133,6 +133,11 @@ class CONTENT_EXPORT RenderFrameHostManager
             int view_routing_id,
             int frame_routing_id);
 
+  // Shutdown all RenderFrameHosts in a SiteInstance. This is called to shutdown
+  // frames when all the frames in a SiteInstance are confirmed to be swapped
+  // out.
+  static void ShutdownRenderFrameHostsInSiteInstance(int32 site_instance_id);
+
   // Returns the currently active RenderFrameHost.
   //
   // This will be non-NULL between Init() and Shutdown(). You may want to NULL
@@ -375,11 +380,6 @@ class CONTENT_EXPORT RenderFrameHostManager
   // since there could be Web UI switching as well. Call this for every commit.
   void CommitPending();
 
-  // Shutdown all RenderFrameHosts in a SiteInstance. This is called to shutdown
-  // frames when all the frames in a SiteInstance are confirmed to be swapped
-  // out.
-  void ShutdownRenderFrameHostsInSiteInstance(int32 site_instance_id);
-
   // Helper method to terminate the pending RenderViewHost.
   void CancelPending();