Fixing gm build with SkXPSDevice enabled

REVIEW=http://codereview.appspot.com/5981054/



git-svn-id: http://skia.googlecode.com/svn/trunk@3591 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gyp/xps.gyp b/gyp/xps.gyp
index 5249c16..1337fd3 100644
--- a/gyp/xps.gyp
+++ b/gyp/xps.gyp
@@ -51,6 +51,7 @@
         ],
         'include_dirs': [
           '../include/device/xps',
+          '../src/utils', # needed to get SkBitSet.h
         ],
       },
     },