Cleanup test_support target names.

Cleanup test_support target names.

In GN it is redundat to include the parent directory name, as in
ui/gfx:gfx_test_support. Instead we can write it as ui/gfx:test_support
which is shorter and nicer to read.

Targets found with the following command line:
$ for f in $(g ls-files | grep BUILD); do grep _test_support $f; echo
$f; done

BUG=None
TEST=None
R=brettw@chromium.org
TBR=darin@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=284800

[brettw, 2014-07-21 04:33:22]

Nice LGTM

[tfarina, 2014-07-22 23:27:11]

Committed patchset #1 manually as r284800 (presubmit successful).