Avoid layout when list color changes

Previously when the style of list item changes, we reset style of
the list marker, causing unnecessary change of margins (which are reset
to initial value) and unnecessary layout.

Let the new style use the original margins to avoid the unnecessary
change.

BUG=397956
TEST=fast/lists/list-color-change-no-layout.html

Review URL: https://codereview.chromium.org/644073002

git-svn-id: svn://svn.chromium.org/blink/trunk@183763 bbb929c8-8fbe-4397-9dbb-9b2b20218538