Revert of ui: Move ui_unittests.gyp into ui/base. (patchset #5 id:80001 of https://codereview.chromium.org/506483002/)

Reason for revert:
it breaks clobber build of ios_dbg_simulator.

Original issue's description:
> ui: Move ui_unittests.gyp into ui/base.
>
> ui_unittests.gyp -> ui_base_tests.gyp (follow gfx_tests.gyp pattern).
> ui_unittests_bundle.gypi -> ui/base/ui_base_tests_bundle.gypi
> ui_unittests.isolate -> ui_base_tests.isolate
>
> Add a TODO assigned to me to rename ui_unittests target to
> ui_base_unittests when buildbot is updated.
>
> BUG=331829,373148,299841,103304
> TEST=ui_unittests
> R=sky@chromium.org
>
> Committed: https://chromium.googlesource.com/chromium/src/+/60f6892f7223f9d6db92314edb5df9b63d25720f

TBR=sky@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=331829,373148,299841,103304

Review URL: https://codereview.chromium.org/522843002

Cr-Commit-Position: refs/heads/master@{#292657}
7 files changed