Have each SandboxedProcessLauncherDelegate maintain a zygote.

components/nacl/browser/nacl_process_host.cc

 // Copyright (c) 2012 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 "components/nacl/browser/nacl_process_host.h"
 
 #include <string.h>
 #include <algorithm>
 #include <string>
 #include <utility>
@@ skipping 163 matching lines @@
     // from .dll loading. The NaCl process will attempt to locate this space by
     // scanning the address space using VirtualQuery.
     // TODO(bbudge) Handle the --no-sandbox case.
     // http://code.google.com/p/nativeclient/issues/detail?id=2131
     const SIZE_T kNaClSandboxSize = 1 << 30;
     if (!nacl::AllocateAddressSpaceASLR(process, kNaClSandboxSize)) {
       DLOG(WARNING) << "Failed to reserve address space for Native Client";
     }
   }
 #elif defined(OS_POSIX)
-  bool ShouldUseZygote() override { return true; }
+#if !defined(OS_MACOSX) && !defined(OS_ANDROID)
+  content::ZygoteHandle* GetZygote() override {
+    static content::ZygoteHandle zygote;

[Mark Seaborn, 2016/01/11 22:42:39]

Does this mean the zygote process is launched on demand?  Doesn't that break
auto-update via Linux package managers (as described in
http://neugierig.org/software/chromium/notes/2011/08/zygote.html)?

[mdempsky, 2016/01/11 22:50:28]

Yes.  I'm not convinced that's a problem per se (see below), but perhaps we
should try to launch all of the zygote processes at startup for now, and change
to on-demand for non-critical zygotes in a separate CL.
It does.  However, at least my anecdotal experience with Chrome on Linux in
recent history is that we don't handle Chrome being updated on disk underneath
us very gracefully anyway.  Whenever the hot-dog-update icon appears for me,
Chrome becomes super laggy and crashy anyway, and I *have* to reboot to get even
basic things like Gmail and YouTube usable again.

+    return &zygote;
+  }
+#endif  // !defined(OS_MACOSX) && !defined(OS_ANDROID)
+
   base::ScopedFD TakeIpcFd() override { return std::move(ipc_fd_); }
 #endif  // OS_WIN
 
  private:
 #if defined(OS_POSIX)
   base::ScopedFD ipc_fd_;
 #endif  // OS_POSIX
 };
 
 void SetCloseOnExec(NaClHandle fd) {
@@ skipping 1178 matching lines @@
     NaClStartDebugExceptionHandlerThread(
         process.Pass(), info, base::ThreadTaskRunnerHandle::Get(),
         base::Bind(&NaClProcessHost::OnDebugExceptionHandlerLaunchedByBroker,
                    weak_factory_.GetWeakPtr()));
     return true;
   }
 }
 #endif
 
 }  // namespace nacl