Have each SandboxedProcessLauncherDelegate maintain a zygote.

content/browser/utility_process_host_impl.cc

Index: content/browser/utility_process_host_impl.cc
diff --git a/content/browser/utility_process_host_impl.cc b/content/browser/utility_process_host_impl.cc
index 4cd0cd19e9318a0a549a5ff4e376538fb49b50c1..d34e0883498eb1a62ebeb901a5e949a978bc59d0 100644
--- a/content/browser/utility_process_host_impl.cc
+++ b/content/browser/utility_process_host_impl.cc
@@ -86,8 +86,12 @@ class UtilitySandboxedProcessLauncherDelegate
 
 #elif defined(OS_POSIX)
 
-  bool ShouldUseZygote() override {
-    return !no_sandbox_ && exposed_dir_.empty();
+  ZygoteHandle* GetZygote() override {
+    if (!no_sandbox_ && exposed_dir_.empty()) {
+      static ZygoteHandle zygote;
+      return &zygote;
+    }
+    return nullptr;
   }
   base::EnvironmentMap GetEnvironment() override { return env_; }
   base::ScopedFD TakeIpcFd() override { return std::move(ipc_fd_); }