Copy the M_THREAD_DISABLE_MEM_INIT constant value into malloc.h.

This will allow platform and application developers to use it.

Bug: 163630045
Change-Id: If9a361cb97aaf62d3fa124b60f64d51d609af48d
diff --git a/tests/malloc_test.cpp b/tests/malloc_test.cpp
index 55bd149..d692cf9 100644
--- a/tests/malloc_test.cpp
+++ b/tests/malloc_test.cpp
@@ -84,6 +84,24 @@
   free(ptr);
 }
 
+TEST(malloc, calloc_mem_init_disabled) {
+#if defined(__BIONIC__)
+  // calloc should still zero memory if mem-init is disabled.
+  // With jemalloc the mallopts will fail but that shouldn't affect the
+  // execution of the test.
+  mallopt(M_THREAD_DISABLE_MEM_INIT, 1);
+  size_t alloc_len = 100;
+  char *ptr = reinterpret_cast<char*>(calloc(1, alloc_len));
+  for (size_t i = 0; i < alloc_len; i++) {
+    ASSERT_EQ(0, ptr[i]);
+  }
+  free(ptr);
+  mallopt(M_THREAD_DISABLE_MEM_INIT, 0);
+#else
+  GTEST_SKIP() << "bionic-only test";
+#endif
+}
+
 TEST(malloc, calloc_illegal) {
   SKIP_WITH_HWASAN;
   errno = 0;