Fix BOM handling w/ bookmark + streaming parsing.

Fix BOM handling w/ bookmark + streaming parsing.

Previously, resetting a bookmark in a file with BOM would not account for
the BOM length, meaning the parser would be off by 2 (UCS2) or 3 (UTF-8)
bytes. Additional information in the comments and in the referenced bug.

It's not an off-by-1 error, it's an off-by-O(1) error.

R=jochen@chromium.org
BUG=527930
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=201915

[jochen (gone - plz use gerrit), 2015-09-08 12:20:43]

lgtm

[vogelheim, 2015-09-08 13:35:49]

The CQ bit was checked by vogelheim@chromium.org

[commit-bot: I haz the power, 2015-09-08 13:35:58]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1315873003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1315873003/1

[commit-bot: I haz the power, 2015-09-08 14:45:55]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=201915