[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 768532a889c72382c1f8c9d78d27ec7e963973a9..6e38bdeb93e9b904c12e1c11acd064cf6e7d019f 100644
--- a/content/browser/frame_host/render_frame_host_manager.h
+++ b/content/browser/frame_host/render_frame_host_manager.h
@@ -275,6 +275,11 @@ class CONTENT_EXPORT RenderFrameHostManager
   void ClearPendingShutdownRFHForSiteInstance(int32 site_instance_id,
                                               RenderFrameHostImpl* rfh);
 
+  // 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);
+
  private:
   friend class RenderFrameHostManagerTest;
   friend class TestWebContents;
@@ -378,11 +383,6 @@ 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();