It sucks that nsIRegistry has to always allocate and return
 strings. nsIRegistryGetter adds in interfaces for non allocating getters
 to registry values.
[uuid(3a15fc88-7a61-4ab4-8e58-31e95fab3da8)]
interface nsIRegistryGetter : nsISupports

Methods

 Get a a byte array value of attribute valname

 @return
  NS_OK on success. buf has the string value copied into it.
    length is updated to actual number of bytes copied into buf.
  NS_ERROR_REG_BUFFER_TOO_SMALL if not enough buffer space.
    length is updated to actual length in PRUint8s including
    terminating NULL and buf will be unchanged.
  NS_ERROR_FAILURE if an unknown error happened. state of buf and
    length undefined.
  various other failure codes otherwise. buf and length wont be updated.
void getBytesUTF8IntoBuffer(in nsRegistryKey baseKey, in string path, inout PRUint8 buf, inout PRUint32 length) 
 Get a string value of attribute valname in widestring or utf8 format

 @return
  NS_OK on success.
    buf has the string value copied into it. length is NOT changed.
  NS_ERROR_REG_BUFFER_TOO_SMALL if not enough buffer space.
    length is updated to actual length in chars including
    terminating NULL and buf will be unchanged.
  NS_ERROR_FAILURE if an unknown error happened. state of buf and
    length undefined.
  various failure codes otherwise. buf and length wont be updated.
void getStringUTF8IntoBuffer(in nsRegistryKey baseKey, in string path, inout char buf, inout PRUint32 length)