adb: fix socket tests.

Bug: 28386497

Change-Id: I9f37ecadf3cfc6bb4e5da502d40f49e1f3a16d8a
diff --git a/adb/fdevent_test.h b/adb/fdevent_test.h
index c853bce..ef65b74 100644
--- a/adb/fdevent_test.h
+++ b/adb/fdevent_test.h
@@ -49,6 +49,16 @@
         dummy = dummy_fds[0];
     }
 
+    size_t GetAdditionalLocalSocketCount() {
+#if ADB_HOST
+        // dummy socket installed in PrepareThread()
+        return 1;
+#else
+        // dummy socket and one more socket installed in fdevent_subproc_setup()
+        return 2;
+#endif
+    }
+
     void TerminateThread(adb_thread_t thread) {
         fdevent_terminate_loop();
         ASSERT_TRUE(WriteFdExactly(dummy, "", 1));