Keep NaCl plugins used in app background pages alive when active.

chrome/browser/nacl_host/nacl_browser_delegate_impl.h

Index: chrome/browser/nacl_host/nacl_browser_delegate_impl.h
diff --git a/chrome/browser/nacl_host/nacl_browser_delegate_impl.h b/chrome/browser/nacl_host/nacl_browser_delegate_impl.h
index c23fefcbd886747e5a6f7745356cc1969a65ba12..674d517cdffd4ceafb21d55ed8ad637404170ef8 100644
--- a/chrome/browser/nacl_host/nacl_browser_delegate_impl.h
+++ b/chrome/browser/nacl_host/nacl_browser_delegate_impl.h
@@ -29,6 +29,8 @@ class NaClBrowserDelegateImpl : public NaClBrowserDelegate {
                                      base::FilePath* file_path) OVERRIDE;
   virtual void SetDebugPatterns(std::string debug_patterns) OVERRIDE;
   virtual bool URLMatchesDebugPatterns(const GURL& manifest_url) OVERRIDE;
+  virtual content::BrowserPpapiHost::OnKeepaliveCallback
+      GetOnKeepaliveCallback() OVERRIDE;
 
  private:
   scoped_refptr<extensions::InfoMap> extension_info_map_;