Implement SkAshmemDiscardableMemory

src/utils/android/ashmem.h

Index: src/utils/android/ashmem.h
diff --git a/src/utils/android/ashmem.h b/src/utils/android/ashmem.h
index 278192b4399ec5fb946d7bba8db151a775159626..94ffe1a33b6f66594a604431c25c05370f7e5dd1 100644
--- a/src/utils/android/ashmem.h
+++ b/src/utils/android/ashmem.h
@@ -16,6 +16,12 @@ extern "C" {
 
 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);