Only use SiteInstance process reuse for ServiceWorker with no failures

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 b7fbe590ba6c1bc747066ef2c9f6c6d26fe3bfdd..12a336ac1cc57d375546b501ef11813e77e9e6dd 100644
--- a/content/browser/service_worker/service_worker_process_manager.cc
+++ b/content/browser/service_worker/service_worker_process_manager.cc
@@ -216,14 +216,17 @@ void ServiceWorkerProcessManager::AllocateWorkerProcess(
     }
   }
 
-  // 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