Add required CUPS include.

BUG=none

Review URL: http://codereview.chromium.org/8805005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@113180 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/printing/print_system_task_proxy_unittest.cc

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 #include <cups/cups.h>
+#include <cups/ppd.h>
 
 #include <cstring>
 #include <string>