EnumTraits for base::i18n::TextDirection.

Moves EnumTraits for base::i18n::TextDirection from autofill_types.mojom
to mojo/common/rtl.mojom so IME can also use it.

This also removes TEXT_DIRECTION_NUM_DIRECTIONS and introduces
TEXT_DIRECTION_MAX = LEFT_TO_RIGHT, to avoid having an extra unnecessary
case in switch statements on TextDirection.

BUG=NONE

Review-Url: https://codereview.chromium.org/2626093004
Cr-Commit-Position: refs/heads/master@{#443736}
15 files changed