Have each SandboxedProcessLauncherDelegate maintain a zygote.

content/browser/utility_process_host_impl.h

Index: content/browser/utility_process_host_impl.h
diff --git a/content/browser/utility_process_host_impl.h b/content/browser/utility_process_host_impl.h
index 94aafa7c51732d6ad07a92d0dc51bd959efeedd1..46dc6bf2486f91282c3587efabd3a6f9f65d7915 100644
--- a/content/browser/utility_process_host_impl.h
+++ b/content/browser/utility_process_host_impl.h
@@ -63,6 +63,11 @@ class CONTENT_EXPORT UtilityProcessHostImpl
 
   void set_child_flags(int flags) { child_flags_ = flags; }
 
+#if defined(OS_POSIX) && !defined(OS_ANDROID) && !defined(OS_MACOSX)
+  // Launch the zygote early in the browser startup.
+  static void EarlyZygoteLaunch();
+#endif  // defined(OS_POSIX) && !defined(OS_ANDROID) && !defined(OS_MACOSX)
+
  private:
   // Starts a process if necessary.  Returns true if it succeeded or a process
   // has already been started via StartBatchMode().