AU: Don't request data ranges beyond the end of the payload.

AU: Don't request data ranges beyond the end of the payload.

This avoids 416 HTTP response error codes from the server. Note that even
without this change update would eventually succeed due to more than 10 resume
failures (so the safety net actually worked).

BUG=8017
TEST=unit tests; tested on device by first reproducing the issue by
interrupting an update during the finalizing step and then getting 416,
then verified the patch resumes the update. Also, verified updates
interrupted in the middle of the download resume correctly.

Change-Id: Iede50a8f8a9d6c000cfeb03308e9ea4f3db74e1b

Committed: http://chrome-svn/viewvc/chromeos?view=rev&revision=b21ce5d

[adlr, 2010-10-21 22:58:08]

LGTM