Allow site authors to override autofilled fields' colors.

Allow site authors to override autofilled fields' colors.
https://bugs.webkit.org/show_bug.cgi?id=66032
http://code.google.com/p/chromium/issues/detail?id=46543

Reviewed by Simon Fraser.

Source/WebCore:

* css/html.css:
(input:-webkit-autofill): Remove !important declarations.

LayoutTests:

* fast/forms/input-autofilled-expected.txt:
* fast/forms/input-autofilled.html:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@113511 268f45cc-cd09-0410-ab3c-d52691b4dbfc