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

ppapi/proxy/plugin_globals.cc

Index: ppapi/proxy/plugin_globals.cc
diff --git a/ppapi/proxy/plugin_globals.cc b/ppapi/proxy/plugin_globals.cc
index fa5530e4390f53022ca2e22f8192d0ec237e7b67..0c66804b106ebb5b0137f8ed3108c78b45a44edd 100644
--- a/ppapi/proxy/plugin_globals.cc
+++ b/ppapi/proxy/plugin_globals.cc
@@ -51,7 +51,8 @@ PluginGlobals* PluginGlobals::plugin_globals_ = NULL;
 PluginGlobals::PluginGlobals()
     : ppapi::PpapiGlobals(),
       plugin_proxy_delegate_(NULL),
-      callback_tracker_(new CallbackTracker) {
+      callback_tracker_(new CallbackTracker),
+      plugin_has_been_active_(true) {
   DCHECK(!plugin_globals_);
   plugin_globals_ = this;
 
@@ -160,6 +161,10 @@ base::TaskRunner* PluginGlobals::GetFileTaskRunner() {
   return file_thread_->message_loop_proxy();
 }
 
+void PluginGlobals::MarkPluginIsActive() {
+  plugin_has_been_active_ = true;
+}
+
 IPC::Sender* PluginGlobals::GetBrowserSender() {
   if (!browser_sender_.get()) {
     browser_sender_.reset(