Move SkOSFile::Iter impls into ports.

src/ports/SkOSFile_none.cpp

-/*
- * Copyright 2013 Google Inc.
- *
- * Use of this source code is governed by a BSD-style license that can be
- * found in the LICENSE file.
- */
-
-#include "SkOSFile.h"
-
-bool sk_exists(const char *path, SkFILE_Flags flags) {
-    return false;
-}
-
-bool sk_fidentical(SkFILE* a, SkFILE* b) {
-    return false;
-}
-
-int sk_fileno(SkFILE* f) {
-    return -1;
-}
-
-void sk_fmunmap(const void* addr, size_t length) { }
-
-void* sk_fdmmap(int fd, size_t* size) {
-    return NULL;
-}
-
-void* sk_fmmap(SkFILE* f, size_t* size) {
-    return NULL;
-}