cros-garcon: Create /usr/share/desktop-directories

This fixes a bug with xdg-desktop-menu where it needs that directory to
exist if it is installing a system desktop menu file.

BUG=chromium:871841
TEST=Verified installer creates the directory
CQ-DEPEND=CL:1191866

Change-Id: If63c772c323df09b52a357de817bd35552526145
Reviewed-on: https://chromium-review.googlesource.com/1191867
Commit-Ready: Jeffrey Kardatzke <jkardatzke@google.com>
Tested-by: Jeffrey Kardatzke <jkardatzke@google.com>
Reviewed-by: Stephen Barber <smbarber@chromium.org>
diff --git a/cros-garcon/BUILD b/cros-garcon/BUILD
index ad29f47..db51940 100644
--- a/cros-garcon/BUILD
+++ b/cros-garcon/BUILD
@@ -87,7 +87,7 @@
     maintainer = "The Chromium OS Authors <chromium-os-dev@chromium.org>",
     package = "cros-garcon",
     depends = ["desktop-file-utils","packagekit","xdg-utils"],
-    version = "0.17",
+    version = "0.18",
     section = "misc",
     conffiles_file = "conffiles",
     postinst = "postinst",
diff --git a/cros-garcon/postinst b/cros-garcon/postinst
index 6b19dca..3fa4ca2 100644
--- a/cros-garcon/postinst
+++ b/cros-garcon/postinst
@@ -23,3 +23,5 @@
     fi
   fi
 done
+# Make xdg-desktop-menu happy when installing system desktop files.
+mkdir -p /usr/share/desktop-directories