Make SandboxIPCProcess a thread.

content/browser/zygote_host/zygote_host_impl_linux.h

 // 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.
 
 #ifndef CONTENT_BROWSER_ZYGOTE_HOST_ZYGOTE_HOST_IMPL_LINUX_H_
 #define CONTENT_BROWSER_ZYGOTE_HOST_ZYGOTE_HOST_IMPL_LINUX_H_
 
 #include <set>
 #include <string>
 #include <vector>
@@ skipping 37 matching lines @@
   // still running, even when they're not. When |known_dead| is true, the
   // process will be SIGKILL-ed first (which should have no effect if it was
   // really dead). This is to prevent a waiting waitpid() from blocking in
   // a single-threaded Zygote. See crbug.com/157458.
   base::TerminationStatus GetTerminationStatus(base::ProcessHandle handle,
                                                bool known_dead,
                                                int* exit_code);
 
   // ZygoteHost implementation:
   virtual pid_t GetPid() const OVERRIDE;
-  virtual pid_t GetSandboxHelperPid() const OVERRIDE;
   virtual int GetSandboxStatus() const OVERRIDE;
   virtual void AdjustRendererOOMScore(base::ProcessHandle process_handle,
                                       int score) OVERRIDE;
 
  private:
   friend struct DefaultSingletonTraits<ZygoteHostImpl>;
 
   ZygoteHostImpl();
   virtual ~ZygoteHostImpl();
 
@@ skipping 28 matching lines @@
   // A lock protecting list_of_running_zygote_children_ and
   // should_teardown_after_last_child_exits_.
   base::Lock child_tracking_lock_;
   std::set<pid_t> list_of_running_zygote_children_;
   bool should_teardown_after_last_child_exits_;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_ZYGOTE_HOST_ZYGOTE_HOST_IMPL_LINUX_H_