Autofill/rAc: dispatch "input" events when changing text contents of <textarea>,
<select>, or <input> tags via Autofill.

This more closely matches the spec behavior as "input" events should be fired
whenever the text is changed.  From the spec[1]:

"""
When the user agent is to change an input element's value on behalf of the user
(e.g. as part of a form prefilling feature), the user agent must queue a task to
first update the value accordingly, then fire a simple event that bubbles named
input at the input element, then fire a simple event that bubbles named change
at the input element.
"""

BUG=353691
R=tkent@chromium.org

[1] http://www.whatwg.org/specs/web-apps/current-work/multipage/common-input-element-attributes.html#event-input-input

Review URL: https://codereview.chromium.org/215903003

git-svn-id: svn://svn.chromium.org/blink/trunk@170278 bbb929c8-8fbe-4397-9dbb-9b2b20218538