On changes, run the gtest_extras unit tests.

Test: atest gtest_isolated_tests
Change-Id: I83e514ae64b1aeece09799670d7390699f5231d6
diff --git a/TEST_MAPPING b/TEST_MAPPING
new file mode 100644
index 0000000..c4002f2
--- /dev/null
+++ b/TEST_MAPPING
@@ -0,0 +1,7 @@
+{
+  "presubmit": [
+    {
+      "name": "gtest_isolated_tests"
+    }
+  ]
+}