[not part of build] Added GetFile() to implement the file attribute.

netwerk/cache/src/nsCacheEntryDescriptor.cpp

@@ -260,6 +260,14 @@ nsCacheEntryDescriptor::SetStoragePolicy(nsCacheStoragePolicy policy)
     return NS_ERROR_NOT_IMPLEMENTED;
 }
 
+NS_IMETHODIMP
+nsCacheEntryDescriptor::GetFile(nsIFile ** result)
+{
+    NS_ENSURE_ARG_POINTER(result);
+    if (!mCacheEntry)  return NS_ERROR_NOT_AVAILABLE;
+    
+    return NS_ERROR_NOT_IMPLEMENTED;
+}
 
 NS_IMETHODIMP
 nsCacheEntryDescriptor::Doom()