Use a single, generic, global zygote to temporarily resolve perf regressions.

content/browser/zygote_host/zygote_handle_linux.cc

 // Copyright 2016 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/public/browser/zygote_handle_linux.h"
 
 #include "content/browser/zygote_host/zygote_communication_linux.h"
 
 namespace content {
 
 ZygoteHandle CreateZygote() {
   ZygoteHandle zygote = new ZygoteCommunication();
   zygote->Init();
   return zygote;
 }
 
+ZygoteHandle* GetGenericZygote() {
+  static ZygoteHandle zygote;
+  return &zygote;
+}
+
 }  // namespace content