Add mount sources for a MountNode (inode)

native_client_sdk/src/libraries/nacl_mounts/mount_node.h

Index: native_client_sdk/src/libraries/nacl_mounts/mount_node.h
===================================================================
--- native_client_sdk/src/libraries/nacl_mounts/mount_node.h	(revision 134714)
+++ native_client_sdk/src/libraries/nacl_mounts/mount_node.h	(working copy)
@@ -23,7 +23,7 @@
  protected:
   MountNode(Mount* mount, int ino, int dev);
   virtual bool Init(int mode, short uid, short gid);
-  virtual void Destroy();
+  virtual int Close();
 
 public:
   // Normal OS operations on a node (file), can be called by the kernel
@@ -55,6 +55,7 @@
 
   // Find a child and return it without updating the refcount
   virtual MountNode* FindChild(const std::string& name);
+  virtual int ChildCount();
 
   // Update the link count
   virtual void Link();
@@ -64,7 +65,8 @@
   struct stat stat_;
   Mount* mount_;
 
-  friend class Mount;
+  friend class MountHFS;
+  friend class MountMem;
   friend class MountNodeDir;
 };