Clean up ChildProcessHost unique id generation.

content/public/common/child_process_host.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_PULIC_COMMON_CHILD_PROCESS_HOST_H_
 #define CONTENT_PULIC_COMMON_CHILD_PROCESS_HOST_H_
 
 #include "build/build_config.h"
 #include "content/common/content_export.h"
 #include "ipc/ipc_channel_proxy.h"
 
 namespace base {
 class FilePath;
 }
 
 namespace content {
 
 class ChildProcessHostDelegate;
 
 // This represents a non-browser process. This can include traditional child
 // processes like plugins, or an embedder could even use this for long lived
 // processes that run independent of the browser process.
 class CONTENT_EXPORT ChildProcessHost : public IPC::Sender {
  public:
   virtual ~ChildProcessHost() {}
 
+  // This is a value never returned as the unique id of any child processes of
+  // any kind, including the values returned by RenderProcessHost::GetID().
+  static int kInvalidUniqueID;
+
   // Used to create a child process host. The delegate must outlive this object.
-  static ChildProcessHost* Create(
-      ChildProcessHostDelegate* delegate);
+  static ChildProcessHost* Create(ChildProcessHostDelegate* delegate);
 
   // These flags may be passed to GetChildPath in order to alter its behavior,
   // causing it to return a child path more suited to a specific task.
   enum {
     // No special behavior requested.
     CHILD_NORMAL = 0,
 
 #if defined(OS_LINUX)
     // Indicates that the child execed after forking may be execced from
     // /proc/self/exe rather than using the "real" app path. This prevents
@@ skipping 51 matching lines @@
 
 #if defined(OS_POSIX)
   // See IPC::Channel::TakeClientFileDescriptor.
   virtual int TakeClientFileDescriptor() = 0;
 #endif
 };
 
 };  // namespace content
 
 #endif  // CONTENT_PULIC_COMMON_CHILD_PROCESS_HOST_H_