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

components/nacl/browser/nacl_process_host.cc

Index: components/nacl/browser/nacl_process_host.cc
diff --git a/components/nacl/browser/nacl_process_host.cc b/components/nacl/browser/nacl_process_host.cc
index 2d154f38d986a846756618da10884de75f8dd870..a0868b8e1bb152187d94ccd93a60626b7263e957 100644
--- a/components/nacl/browser/nacl_process_host.cc
+++ b/components/nacl/browser/nacl_process_host.cc
@@ -49,6 +49,7 @@
 #include "ppapi/host/ppapi_host.h"
 #include "ppapi/proxy/ppapi_messages.h"
 #include "ppapi/shared_impl/ppapi_nacl_channel_args.h"
+#include "ppapi/shared_impl/ppapi_switches.h"
 
 #if defined(OS_POSIX)
 #include <fcntl.h>
@@ -799,6 +800,8 @@ void NaClProcessHost::OnPpapiChannelCreated(
         nacl_host_message_filter_->render_process_id(),
         render_view_id_,
         profile_directory_));
+    ppapi_host_->SetOnKeepaliveCallback(
+        NaClBrowser::GetDelegate()->GetOnKeepaliveCallback());
 
     ppapi::PpapiNaClChannelArgs args;
     args.off_the_record = nacl_host_message_filter_->off_the_record();