previousRegionLogicalHeight not getting updated

previousRegionLogicalHeight() was not getting updated in RenderFlowThread::validateRegions() and 
previousRegionLogicalWidth() was updated but not used.

Review URL: https://codereview.chromium.org/147653002

git-svn-id: svn://svn.chromium.org/blink/trunk@170589 bbb929c8-8fbe-4397-9dbb-9b2b20218538