Checking out of bound position in RenderBlock::positionForPoint

This patch changes RenderBlock::positionForPoint() to check out of bound position. When document is no quirk mode, RenderBlock::positionForPoint() gets a position which is out side of RenderBlock due by closestBox->root()->blockDirectionPointInLine() in RenderBlock::positionForPointWithInlineChildren() returns RootInLineBox.logicalTop() which is smaller than closestBox.logicalTop().

BUG=256989
R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/21780002

git-svn-id: svn://svn.chromium.org/blink/trunk@157506 bbb929c8-8fbe-4397-9dbb-9b2b20218538