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

Review URL: https://codereview.chromium.org/506483002

Cr-Commit-Position: refs/heads/master@{#292146}
7 files changed