The last numeric field of input[type=date] should not accept huge values by keyboard input.

The code assumed we moved focus to the next field if a field is filled.
However we can't move focus if the field is the last one.

We remove leading digits in the buffer if a digit is typed and the field
is filled.

BUG=239377

Review URL: https://codereview.chromium.org/118983002

git-svn-id: svn://svn.chromium.org/blink/trunk@164159 bbb929c8-8fbe-4397-9dbb-9b2b20218538