Re-commit r22981 after backout at r22992

chrome/common/child_process_host.h

Index: chrome/common/child_process_host.h
===================================================================
--- chrome/common/child_process_host.h	(revision 22996)
+++ chrome/common/child_process_host.h	(working copy)
@@ -22,6 +22,13 @@
  public:
   virtual ~ChildProcessHost();
 
+  // Returns the pathname to be used for a child process.  If a subprocess
+  // pathname was specified on the command line, that will be used.  Otherwise,
+  // the default child process pathname will be returned.  On most platforms,
+  // this will be the same as the currently-executing process.  On failure,
+  // returns an empty wstring.
+  static std::wstring GetChildPath();
+
   // ResourceDispatcherHost::Receiver implementation:
   virtual bool Send(IPC::Message* msg);