Fill list style background with same color with that of list background.

LayoutListMarker does not have a node so its selectionBackgroundColor alway returns
the default theme color for selection. We can make it more natural by filling
the same color with that of LayoutListItem into it.

BUG=467092

Review URL: https://codereview.chromium.org/1063453002

git-svn-id: svn://svn.chromium.org/blink/trunk@193335 bbb929c8-8fbe-4397-9dbb-9b2b20218538
8 files changed