Add HTMLInputType::m_inputTypeView.

InputTypeView functions are called through m_inputTypeView though
m_inputTypeView is identical to m_inputType for now.

This is a preparation to support author shadow DOM for INPUT elements.

BUG=274205
TEST=none; no behavior changes.

Review URL: https://chromiumcodereview.appspot.com/23458005

git-svn-id: svn://svn.chromium.org/blink/trunk@156844 bbb929c8-8fbe-4397-9dbb-9b2b20218538