hr color attribute not working.

The noshade attribute is a boolean attribute and when set on hr element
it shows a gray color. When there is color attribute the default gray
color should be replaced by the color mentioned by the color attribute.
Firefox and IE show the same behaviour but Blink is different. Making
the behaviour of Blink similiar to Firefox and IE's behaviour.

When the color attribute is present that value is applied and the
default gray color is ignored. Incase of no color attribute the default
gray color is applied.

I already landed this patch on Webkit. Just modified the layout test file.
http://trac.webkit.org/changeset/161334

R=esprehn@chromium.org,eseidel@chromium.org
BUG=175359

Review URL: https://codereview.chromium.org/162993002

git-svn-id: svn://svn.chromium.org/blink/trunk@168571 bbb929c8-8fbe-4397-9dbb-9b2b20218538