Reviewed by John Sullivan.

        <rdar://problem/4663772> REGRESSION: Cannot type in Japanese after replying to a particular message
        <rdar://problem/4673293> REGRESSION: Can't enter the Japanese characters in Mail or Blot

        * fast/text/attributed-substring-from-range-001-expected.txt: Added.
        * fast/text/attributed-substring-from-range-001.html: Added.
        
        Check attributed string results when starting or ending at a br element.

WebCore:

        Reviewed by John Sullivan.

        <rdar://problem/4663772> REGRESSION: Cannot type in Japanese after replying to a particular message
        <rdar://problem/4673293> REGRESSION: Can't enter the Japanese characters in Mail or Blot

        Test added
        * fast/text/attributed-substring-from-range-001.html

        * bridge/mac/FrameMac.mm:
        (WebCore::FrameMac::attributedString):
        Handle non-zero offsets when start and/or end node is a container. Offset used to be ignored in this case.
        Also, add validation of the range.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@16642 268f45cc-cd09-0410-ab3c-d52691b4dbfc