libcutils: Add ashmem_valid() function

Bug: 30310689
Change-Id: I14c52c5d52745a725799652b87c86281ac214899
diff --git a/include/cutils/ashmem.h b/include/cutils/ashmem.h
index acedf73..d80caa6 100644
--- a/include/cutils/ashmem.h
+++ b/include/cutils/ashmem.h
@@ -20,6 +20,7 @@
 extern "C" {
 #endif
 
+int ashmem_valid(int fd);
 int ashmem_create_region(const char *name, size_t size);
 int ashmem_set_prot_region(int fd, int prot);
 int ashmem_pin_region(int fd, size_t offset, size_t len);