Fix preferred width calculation for nodes with mixed directionality

Fix a bug in RenderText::computePreferredLogicalWidths where the first
character of a run was incorrectly considered to be part of the
preceding run due to an off-by-one error in the character to run logic.

Also change the BidiResolver initial status to use the node direction.

R=leviw@chromium.org
BUG=373433
TEST=fast/text/mixed-direction-bidi-wrap.html

Review URL: https://codereview.chromium.org/412603002

git-svn-id: svn://svn.chromium.org/blink/trunk@178688 bbb929c8-8fbe-4397-9dbb-9b2b20218538