Remove CSSPropertyID argument from CSSToStyleMap::mapFill* functions

The CSSPropertyID argument is unused in all the various CSSToStyleMap::mapFill*
functions aside from mapFillImage. We can easily derive it in this case
from the type of the layer, so this patch removes this argument from all
these functions.

Review URL: https://codereview.chromium.org/409763004

git-svn-id: svn://svn.chromium.org/blink/trunk@178667 bbb929c8-8fbe-4397-9dbb-9b2b20218538