Make history expiration more aggressive.

Make history expiration more aggressive.

Since we haven't done anything more with history and some users are experiencing larger than expected history files, we can probably now be more aggressive about deleting stuff that isn't so useful.

I changed a number of thresholds:

 - We now keep full text indexed data for 3 months instead of 12.

 - We now expire auto subframe visits after 3 dats instead of 30. I added the rationale in a comment.

 - We now expire 32 visits per iteration instead of 10. This number is always kind of a guesstimate anyway of balancing overhead of a query versus overhead of a delete. Now that we're moving up some thresholds, we'll have a bunch of history to expire and I would rather get this over with faster than spending hours spinning the CPU every 30 seconds. This will also come up for users that haven't used their browsers in a while.
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=107969

[brettw, 2011-10-29 00:22:04]

This came out of some discussions with Jeff.

I'll do a separate patch to completely skip archiving and delete the old
archived DB (we don't use this for anything useful) and to auto vacuum from time
to time.

[sky, 2011-10-31 14:03:39]

LGTM