Use gyp targets to link in X11 libraries instead of setting -lXfoo

media/cast/cast.gyp

Index: media/cast/cast.gyp
diff --git a/media/cast/cast.gyp b/media/cast/cast.gyp
index 16df8a66f3b92ea8255ce4b5a851f723507ba374..ac90b7c0c54ba9fd31a2056d1897e7fd4a674f5b 100644
--- a/media/cast/cast.gyp
+++ b/media/cast/cast.gyp
@@ -146,14 +146,14 @@
           ],
           'conditions': [
             ['OS == "linux"', {
+              'dependencies': [
+                '<(DEPTH)/build/linux/system.gyp:x11',
+                '<(DEPTH)/build/linux/system.gyp:xext',
+              ],
               'sources': [
                 '<(DEPTH)/media/cast/test/linux_output_window.cc',
                 '<(DEPTH)/media/cast/test/linux_output_window.h',
               ],
-              'libraries': [
-                '-lXext',
-                '-lX11',
-             ],
           }],
           ],
         },