Have each SandboxedProcessLauncherDelegate maintain a zygote.

components/nacl/browser/nacl_process_host.h

Index: components/nacl/browser/nacl_process_host.h
diff --git a/components/nacl/browser/nacl_process_host.h b/components/nacl/browser/nacl_process_host.h
index 88d2978ebb58f56d80d6301745352c1c42ce85ed..59f4995c58e47336264c356e47654433e631cb26 100644
--- a/components/nacl/browser/nacl_process_host.h
+++ b/components/nacl/browser/nacl_process_host.h
@@ -93,6 +93,11 @@ class NaClProcessHost : public content::BrowserChildProcessHostDelegate {
   // Do any minimal work that must be done at browser startup.
   static void EarlyStartup();
 
+#if defined(OS_POSIX) && !defined(OS_ANDROID) && !defined(OS_MACOSX)

[Mark Seaborn, 2016/01/19 21:06:43]

NaCl isn't enabled on Android so you probably don't need the OS_ANDROID check
here (and it could be misleading to have it).  Same in other cases that are
behind !defined(DISABLE_NACL).

[Greg K, 2016/01/19 22:20:16]

Done.

+  // Launch the NaCl zygote early in the browser startup.
+  static void EarlyZygoteLaunch();
+#endif  // defined(OS_POSIX) && !defined(OS_ANDROID) && !defined(OS_MACOSX)
+
   // Specifies throttling time in milliseconds for PpapiHostMsg_Keepalive IPCs.
   static void SetPpapiKeepAliveThrottleForTesting(unsigned milliseconds);