Add support for multiple zygote fork delegates

content/public/common/zygote_fork_delegate_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_PUBLIC_COMMON_ZYGOTE_FORK_DELEGATE_LINUX_H_
 #define CONTENT_PUBLIC_COMMON_ZYGOTE_FORK_DELEGATE_LINUX_H_
 
 #include <unistd.h>
 
 #include <string>
@@ skipping 15 matching lines @@
   // alternative to forking the zygote.  A new delegate is passed in
   // as an argument to ZygoteMain().
   virtual ~ZygoteForkDelegate() {}
 
   // Initialization happens in the zygote after it has been
   // started by ZygoteMain.
   // If |enable_layer1_sandbox| is true, the delegate must enable a
   // layer-1 sandbox such as the setuid sandbox.
   virtual void Init(int sandboxdesc, bool enable_layer1_sandbox) = 0;
 
-  // After Init, supply a UMA_HISTOGRAM_ENUMERATION the delegate
-  // would like to supply on the first fork.
+  // After Init, supply a UMA_HISTOGRAM_ENUMERATION the delegate would like
+  // reported to the browser process.  (Note: Because these reports are
+  // piggy-backed onto fork responses that don't otherwise contain UMA reports,
+  // this method may not be called until much later.)
   virtual void InitialUMA(std::string* uma_name,
                           int* uma_sample,
                           int* uma_boundary_value) = 0;
 
   // Returns 'true' if the delegate would like to handle a given fork
   // request.  Otherwise returns false.  Optionally, fills in uma_name et al
   // with a report the helper wants to make via UMA_HISTOGRAM_ENUMERATION.
   virtual bool CanHelp(const std::string& process_type, std::string* uma_name,
                        int* uma_sample, int* uma_boundary_value) = 0;
 
@@ skipping 27 matching lines @@
   // blocking wait() should be performed. In this case, GetTerminationStatus()
   // will send a SIGKILL to the target process first.
   virtual bool GetTerminationStatus(pid_t pid, bool known_dead,
                                     base::TerminationStatus* status,
                                     int* exit_code) = 0;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_COMMON_ZYGOTE_FORK_DELEGATE_LINUX_H_