constructBidiRunsForSegment:
After CLs 39783004 and 46393003 if an isolated fake run is added it is always replaced with real runs. (I am being a bit conservative keeping the if statement.)
 
BidiResolver::setStatus:
When a BidiStatus is passed to BidiResolver, it needs to have a valid context.

BidiRunList<Run>::reverseRuns:
If reverse runs is called it should have in the least one run.

Review URL: https://codereview.chromium.org/62483002

git-svn-id: svn://svn.chromium.org/blink/trunk@161512 bbb929c8-8fbe-4397-9dbb-9b2b20218538