unit_tests: Fix link error (missing libXi) on Linux
unit_tests: Fix link error (missing libXi) on Linux

unit_tests fails to link due to requirement on libXi. This is implicitly
provided by 'gdk', but unit_tests does not depend on this target. We add
a 'xi' dependency for any target depending on 'x11'.

BUG=63209
TEST=None
(Landing patch for jknotten@chromium.org.)

Review URL: http://codereview.chromium.org/5016001

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@66169 0039d316-1c4b-4281-b951-d872f2087c98

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