[CSS Shapes] Adjust lineTop position to the next available wrapping location at shape-outsides

When we don't have space next to the floating container, but we have space inside the floating-container next
to the defined shape-outside, we should wrap around the shape-outside. This patch fixes the behavior both for
cases when there is no space to fit at the first line, and for the additional lines cases.

BUG=346877

Review URL: https://codereview.chromium.org/180303004

git-svn-id: svn://svn.chromium.org/blink/trunk@167975 bbb929c8-8fbe-4397-9dbb-9b2b20218538