Don't choose a background process when choosing a process for starting a Service Worker.

content/browser/service_worker/service_worker_process_manager.cc

Index: content/browser/service_worker/service_worker_process_manager.cc
diff --git a/content/browser/service_worker/service_worker_process_manager.cc b/content/browser/service_worker/service_worker_process_manager.cc
index a310bcc1770b5ca7ec279ad496b594db7ecaba50..83a32f8b4d1132278d504c2b13838a8ee5e18816 100644
--- a/content/browser/service_worker/service_worker_process_manager.cc
+++ b/content/browser/service_worker/service_worker_process_manager.cc
@@ -28,6 +28,8 @@ static bool IncrementWorkerRefCountByPid(int process_id) {
   RenderProcessHost* rph = RenderProcessHost::FromID(process_id);
   if (!rph || rph->FastShutdownStarted())
     return false;
+  if (static_cast<RenderProcessHostImpl*>(rph)->backgrounded())

[kinuko, 2015/09/30 09:26:15]

nit: could we add a comment (like what you wrote in the issue's description) and
link to the bug if this is intended to be a short term fix?

[horo, 2015/09/30 09:45:37]

Done.

+    return false;
 
   static_cast<RenderProcessHostImpl*>(rph)->IncrementWorkerRefCount();
   return true;