Wrap isActivatedSubmit() in WebFormControlElement

This is related refactoring old Blink code, specifically moving functions in
WebPasswordFormData and WebPasswordFormUtils into chromium side. Inevitably,
HTMLFormControlElement.isActivatedSubmit() that is called in WebPasswordFormData
needs to be exposed to chromium side.

R=gcasto@chromium.org, tkent@chromium.org
BUG=

Review URL: https://codereview.chromium.org/234803004

git-svn-id: svn://svn.chromium.org/blink/trunk@171571 bbb929c8-8fbe-4397-9dbb-9b2b20218538