Add external_storage gid

This gid allows processes full access to public areas of external
storage. This includes the following:
1. EmulatedVolumes: All files and directories excluding the app
specific directories under Android/
2. PublicVolumes: Including 'unreliable' volumes (USB OTG) that are
not typically accesible to ordinary apps

Apps with the MANAGE_EXTERNAL_STORAGE permission will automatically
have this gid

Test: m
Bug: 144914977
Change-Id: I17da0b2367e356edc031d063e214574463afc985
diff --git a/libcutils/include/private/android_filesystem_config.h b/libcutils/include/private/android_filesystem_config.h
index f9a3df9..ff6b036 100644
--- a/libcutils/include/private/android_filesystem_config.h
+++ b/libcutils/include/private/android_filesystem_config.h
@@ -130,6 +130,7 @@
 #define AID_GSID 1074            /* GSI service daemon */
 #define AID_FSVERITY_CERT 1075   /* fs-verity key ownership in keystore */
 #define AID_CREDSTORE 1076       /* identity credential manager service */
+#define AID_EXTERNAL_STORAGE 1077 /* Full external storage access including USB OTG volumes */
 /* Changes to this file must be made in AOSP, *not* in internal branches. */
 
 #define AID_SHELL 2000 /* adb and debug shell user */