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

content/browser/service_worker/service_worker_process_manager.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/service_worker/service_worker_process_manager.h"
 
 #include "content/browser/renderer_host/render_process_host_impl.h"
 #include "content/browser/service_worker/service_worker_context_wrapper.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/site_instance.h"
@@ skipping 10 matching lines @@
     return lhs.second > rhs.second;
   }
 };
 
 }  // namespace
 
 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;
 }
 
 ServiceWorkerProcessManager::ProcessInfo::ProcessInfo(
     const scoped_refptr<SiteInstance>& site_instance)
     : site_instance(site_instance),
       process_id(site_instance->GetProcess()->GetID()) {
 }
@@ skipping 229 matching lines @@
 namespace base {
 // Destroying ServiceWorkerProcessManagers only on the UI thread allows the
 // member WeakPtr to safely guard the object's lifetime when used on that
 // thread.
 void DefaultDeleter<content::ServiceWorkerProcessManager>::operator()(
     content::ServiceWorkerProcessManager* ptr) const {
   content::BrowserThread::DeleteSoon(
       content::BrowserThread::UI, FROM_HERE, ptr);
 }
 }  // namespace base