Add TEST_MAPPING for ahat.

Test: atest --host, in art/tools/ahat directory.
Change-Id: I7932e095bc84cd06d1ed06b67a3e42ee41eb18ed
diff --git a/tools/ahat/TEST_MAPPING b/tools/ahat/TEST_MAPPING
new file mode 100644
index 0000000..603e95d
--- /dev/null
+++ b/tools/ahat/TEST_MAPPING
@@ -0,0 +1,7 @@
+{
+  "presubmit": [
+    {
+      "name": "ahat-tests"
+    }
+  ]
+}