Introduce blink::SelectType

This CL introduces blink::SelectType, blink::MenuListSelectType, and
blink::ListBoxSelectType.
Also, add SelectType::DidSelectOption() to simplify
HTMLSelectElement::SelectOption().

This CL has no behavior changes.

Bug: 1052232
Change-Id: I436cfdd70edf0668b03996b35008ae12f8b6c9c3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2055950
Reviewed-by: Koji Ishii <[email protected]>
Commit-Queue: Kent Tamura <[email protected]>
Cr-Commit-Position: refs/heads/master@{#741383}
5 files changed