Its result has 4 meanings:
- an editable block element for container of mScanStartPoint.
- a topmost inline editable content for container of mScanStartPoint if there
is no editable block parent.
- container of mScanStartPoint if it's a block (either editable or
non-editable).
- container of mScanStartPoint if its parent is not editable and a inline
content.
#1, #2 and editable case of #3 make sense because the results are topmost
editable content in current context. On the other hand, non-editable case
of #3 and #4 are caused by unexpected wrong fallback code.
So, let's make it always returns the content in the former meaning and if
the caller needs the latter one, they should use the container by themselves.
Therefore, for making what's the start of the search, this patch also makes
new method take start content instead of hiding mScanStartPoint from the
callers.