Implement SkAshmemDiscardableMemory

src/utils/android/ashmem.h

 /*
  * Copyright 2008 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef _CUTILS_ASHMEM_H
 #define _CUTILS_ASHMEM_H
 
 #include <stddef.h>
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
 int ashmem_create_region(const char *name, size_t size);
 int ashmem_set_prot_region(int fd, int prot);
+
+/**
+ *   @return ASHMEM_NOT_PURGED if the memory was not purged.
+ *           ASHMEM_WAS_PURGED if the memory was purged.
+ *           -1 on error.
+ */
 int ashmem_pin_region(int fd, size_t offset, size_t len);
 int ashmem_unpin_region(int fd, size_t offset, size_t len);
 int ashmem_get_size_region(int fd);
 int ashmem_purge_all_caches(int fd);
 
 #ifdef __cplusplus
 }
 #endif
 
 #ifndef __ASHMEMIOC /* in case someone included <linux/ashmem.h> too */
 
 #define ASHMEM_NAME_LEN     256
 
 #define ASHMEM_NAME_DEF     "dev/ashmem"
 
 /* Return values from ASHMEM_PIN: Was the mapping purged while unpinned? */
 #define ASHMEM_NOT_PURGED   0
 #define ASHMEM_WAS_PURGED   1
 
 /* Return values from ASHMEM_UNPIN: Is the mapping now pinned or unpinned? */
 #define ASHMEM_IS_UNPINNED  0
 #define ASHMEM_IS_PINNED    1
 
 #endif  /* ! __ASHMEMIOC */
 
 #endif  /* _CUTILS_ASHMEM_H */