Use available width for replaced element with intrinsic ratio but no dimensions

Prior to this patch, we walked up the ancestor chain to find a
specified width for replaced content with intrinsic ratio but no
intrinsic size nor any specified dimensions.

This is clearly wrong when the containing block has no specified width
but an implicitly set width through the constraint equation. In that
case we would walk past the containing block and possible find an
ancestor with specified width to size against.

An other illustration of why it's wrong in the context of a stf
container where we would possibly go outside the stf container to
fetch a width.

Both scenarios illustrated by tests.

After this patch, we instead always use the available width of the
container, to properly size inside a container with no specified size.

http://www.w3.org/TR/CSS2/visudet.html#inline-replaced-width

BUG=387705

Review URL: https://codereview.chromium.org/341773004

git-svn-id: svn://svn.chromium.org/blink/trunk@176929 bbb929c8-8fbe-4397-9dbb-9b2b20218538