Move InputType::createShadowSubtree and destroyShadowSubtree to InputTypeView.

UA shadow DOM should belong to views.
We remove unnecessary UA shadow DOM when an input element gets an author
ShadowRoot.

BUG=306257
TEST=none; no visible behavior changes.

Review URL: https://codereview.chromium.org/61693003

git-svn-id: svn://svn.chromium.org/blink/trunk@161889 bbb929c8-8fbe-4397-9dbb-9b2b20218538