Have each SandboxedProcessLauncherDelegate maintain a zygote.

content/browser/browser_main_loop.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 "content/browser/browser_main_loop.h"
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/feature_list.h"
 #include "base/location.h"
@@ skipping 1016 matching lines @@
 #endif
 
 #if defined(USE_AURA) || defined(OS_MACOSX)
   {
     TRACE_EVENT0("shutdown",
                  "BrowserMainLoop::Subsystem:ImageTransportFactory");
     ImageTransportFactory::Terminate();
   }
 #endif
 
-#if defined(OS_POSIX) && !defined(OS_MACOSX) && !defined(OS_ANDROID)
-  ZygoteHostImpl::GetInstance()->TearDownAfterLastChild();

[mdempsky, 2015/12/22 21:21:33]

You might try landing just this removal first/separately.  I think we've
established that it's okay to remove and the trybots seem happy with it, but I
can imagine some weird CrOS or non-trybot tests might start complaining.  (And
if so, better to just have to revert/re-revert a simple one-line CL than your
entire CL.)

[Greg K, 2016/01/05 21:42:13]

Done.

-#endif  // defined(OS_POSIX) && !defined(OS_MACOSX) && !defined(OS_ANDROID)
-
   // The device monitors are using |system_monitor_| as dependency, so delete
   // them before |system_monitor_| goes away.
   // On Mac and windows, the monitor needs to be destroyed on the same thread
   // as they were created. On Linux, the monitor will be deleted when IO thread
   // goes away.
 #if defined(OS_WIN)
   system_message_window_.reset();
 #elif defined(OS_MACOSX)
   device_monitor_mac_.reset();
 #endif
@@ skipping 422 matching lines @@
   DCHECK(is_tracing_startup_for_duration_);
 
   is_tracing_startup_for_duration_ = false;
   TracingController::GetInstance()->StopTracing(
       TracingController::CreateFileSink(
           startup_trace_file_,
           base::Bind(OnStoppedStartupTracing, startup_trace_file_)));
 }
 
 }  // namespace content