ShellPkg: Fix memory leak when running Shell script.

When we run following script in Shell:
"
for %a run (1 200)
  echo %a
  memmap
endfor
"
We may find memory leak in system. This patch free buffer in 'BufferToFreeList' to avoid this issue.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Qiu Shumin <shumin.qiu@intel.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>


git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@19521 6f19259b-4bc3-4df7-8a09-765794883524

ShellPkg/Application/Shell/Shell.h

@@ -382,5 +382,28 @@ TrimSpaces(
   IN CHAR16 **String
   );
 
+/**
+  
+  Create a new buffer list and stores the old one to OldBufferList  
+
+  @param OldBufferList   The temporary list head used to store the nodes in BufferToFreeList.
+**/
+VOID
+SaveBufferList (
+  OUT LIST_ENTRY     *OldBufferList
+  );
+
+/**
+  Restore previous nodes into BufferToFreeList .
+
+  @param OldBufferList   The temporary list head used to store the nodes in BufferToFreeList.
+**/
+VOID
+RestoreBufferList (
+  IN OUT LIST_ENTRY     *OldBufferList
+  );
+
+
+
 #endif //_SHELL_INTERNAL_HEADER_