Properly handle bottom margin on float with shape-outside

When a float has a shape-outside, inline content must conform to the
shape, not to the margin box. Thus, if a float with shape-outside has a
bottom margin and the shape does not intrude into that margin, then the
inline content should ignore the margin. Before this patch, inline
content would drop below the margin box instead of obeying the shape.

Note that content that should clear the float still clears the margin
box, not the shape's contour.

BUG=260357

Review URL: https://chromiumcodereview.appspot.com/24240021

git-svn-id: svn://svn.chromium.org/blink/trunk@158290 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Auto-rebaseline for r158283

http://src.chromium.org/viewvc/blink?view=revision&revision=158283

TBR=g.czajkowski@samsung.com

Review URL: https://codereview.chromium.org/24496002

git-svn-id: svn://svn.chromium.org/blink/trunk@158291 bbb929c8-8fbe-4397-9dbb-9b2b20218538