Remove the use of overrideLogicalContentHeight from the regions' processing model. This prevents flexbox containers from overriding the height value computed when flowing content into auto-height regions.

BUG=256233

Review URL: https://chromiumcodereview.appspot.com/18319004

git-svn-id: svn://svn.chromium.org/blink/trunk@154928 bbb929c8-8fbe-4397-9dbb-9b2b20218538