Only use SiteInstance process reuse for ServiceWorker with no failures

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 <stddef.h>
 
 #include <algorithm>
 #include <utility>
@@ skipping 198 matching lines @@
       instance_info_.insert(
           std::make_pair(embedded_worker_id, ProcessInfo(process_id)));
       BrowserThread::PostTask(
           BrowserThread::IO, FROM_HERE,
           base::Bind(callback, SERVICE_WORKER_OK, process_id,
                      false /* is_new_process */, settings));
       return;
     }
   }
 
-  // No existing processes available; start a new one.
+  // No existing processes available; start a new one. Attempt to reuse an
+  // existing process if possible.

[falken, 2017/06/06 13:32:43]

Now these sentences read like a contradiction :) How about something like:

// ServiceWorkerProcessManager does not know of any renderer processes that are
available for |pattern|. Create a SiteInstance and ask for a renderer process.
Attempt to reuse an existing process if possible.

[clamy, 2017/06/06 16:37:39]

Done.

   // TODO(clamy): Update the process reuse mechanism above following the
   // implementation of
   // SiteInstanceImpl::ProcessReusePolicy::REUSE_PENDING_OR_COMMITTED_SITE.
   scoped_refptr<SiteInstanceImpl> site_instance =
       SiteInstanceImpl::CreateForURL(browser_context_, script_url);
-  site_instance->set_process_reuse_policy(
-      SiteInstanceImpl::ProcessReusePolicy::REUSE_PENDING_OR_COMMITTED_SITE);
+  if (can_use_existing_process) {
+    site_instance->set_process_reuse_policy(
+        SiteInstanceImpl::ProcessReusePolicy::REUSE_PENDING_OR_COMMITTED_SITE);
+  }
   RenderProcessHost* rph = site_instance->GetProcess();
 
   // This Init() call posts a task to the IO thread that adds the RPH's
   // ServiceWorkerDispatcherHost to the
   // EmbeddedWorkerRegistry::process_sender_map_.
   if (!rph->Init()) {
     LOG(ERROR) << "Couldn't start a new process!";
     BrowserThread::PostTask(
         BrowserThread::IO, FROM_HERE,
         base::Bind(callback, SERVICE_WORKER_ERROR_PROCESS_NOT_FOUND,
@@ skipping 108 matching lines @@
 namespace std {
 // Destroying ServiceWorkerProcessManagers only on the UI thread allows the
 // member WeakPtr to safely guard the object's lifetime when used on that
 // thread.
 void default_delete<content::ServiceWorkerProcessManager>::operator()(
     content::ServiceWorkerProcessManager* ptr) const {
   content::BrowserThread::DeleteSoon(
       content::BrowserThread::UI, FROM_HERE, ptr);
 }
 }  // namespace std