Adjust autofilled property for <search> input and <select> elements

Set value of autofilled property to false in the following cases:
  - Cancel search via cancel button in <search> element.
  - Delete autofilled selected <select> option.

This patch also
  - Merged test case for editing text in autofilled textarea.

R=tkent@chromium.org
BUG=395627

Review URL: https://codereview.chromium.org/537393002

git-svn-id: svn://svn.chromium.org/blink/trunk@181589 bbb929c8-8fbe-4397-9dbb-9b2b20218538