Add missing dependency

No idea how this escaped until now.

Change-Id: I268c8af6f0ae6b20cfbc00d00468c41ac6ac002c
diff --git a/aos/common/common.gyp b/aos/common/common.gyp
index 54617db..ff8cbe2 100644
--- a/aos/common/common.gyp
+++ b/aos/common/common.gyp
@@ -22,6 +22,7 @@
         'once',
         '<(AOS)/linux_code/ipc_lib/ipc_lib.gyp:shared_mem',
         'mutex',
+        '<(EXTERNALS):gtest',
       ],
       'export_dependent_settings': [
         '<(AOS)/linux_code/ipc_lib/ipc_lib.gyp:shared_mem',