Do not dispatch 'change' events during pressing spin buttons for input[type=number].

InputType to triggers change event when not in focus and input event when in focus.
The change event is triggered only when user stops pressing spin button.

R=tkent, keishi1
BUG=155747
TEST=Change event is only trigger when mouse press is stopped. Only 1 change event is triggered when moving out of focus.

Review URL: https://codereview.chromium.org/196933006

git-svn-id: svn://svn.chromium.org/blink/trunk@171006 bbb929c8-8fbe-4397-9dbb-9b2b20218538