Add METADATA to dlmalloc: CC0+PublicDomain=UNENCUMBERED

Bug: 68860345
Bug: 69058154
Bug: 151953481

Test: no code changes
Change-Id: I4d0dd50e5e3f8876159278d23c503f67338ada34
diff --git a/METADATA b/METADATA
new file mode 100644
index 0000000..313792c
--- /dev/null
+++ b/METADATA
@@ -0,0 +1,3 @@
+third_party {
+  license_type: UNENCUMBERED
+}