Don't allow minus width for positioned objects

 If left and right is not auto and left+right is bigger than the containing block width,  the width of positioned element can be calculated as negative value.
But, negative values for width are illegal (by CSS2.1 10.2)

If the width is negative, the ClientRect and the boundingClientRect also have incorrect values.

TEST=fast/css/absolute-position-with-negative-width.html

BUG=383936

Review URL: https://codereview.chromium.org/578723003

git-svn-id: svn://svn.chromium.org/blink/trunk@182292 bbb929c8-8fbe-4397-9dbb-9b2b20218538