Tweaks to improve memory consumption by TopSites. The biggest culprit

Tweaks to improve memory consumption by TopSites. The biggest culprit
seems to repeatedly querying history during this perf test. So, the
biggest gain is made by scaling this back. Here are other tweaks I've
made:

. decrease the page size/cache size of the two DBs. Now that favicons
  doesn't store thumbnails the db doesn't need to be so big.
. Set a cap to the max number of tmp thumnbails maintains.
. Force jpg data vector to be only as big as it needs to be.
. Tweak TopSitesCache so it doesn't end up duplicating so many
  GURLs. This is particularly helpful for long redirect lists.

BUG=61487
TEST=none

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=64837

[brettw, 2010-11-01 21:40:21]

http://codereview.chromium.org/4106014/diff/2001/3002
File chrome/browser/history/top_sites.cc (right):

http://codereview.chromium.org/4106014/diff/2001/3002#newcode208
chrome/browser/history/top_sites.cc:208: // Always remove the existing entry,
that way if we end up with too many
Always remove the existing entry and then add it back. That way...  (I was
initially confused and thought you were just removing them.)

http://codereview.chromium.org/4106014/diff/2001/3002#newcode509
chrome/browser/history/top_sites.cc:509: (*bytes)->data.reserve(data.size());
It doesn't seem like this reserve does anything, shouldn't "=" do the copy in
one fell swoop?

http://codereview.chromium.org/4106014/diff/2001/3002#newcode846
chrome/browser/history/top_sites.cc:846: timer_start_time_ = base::Time::Now();
Can this be converted to use TimeTicks to avoid weird effects if the wall clock
changes?

[sky, 2010-11-01 22:04:55]

All updated with new snapshot uploaded.

  -Scott

[brettw, 2010-11-01 22:30:06]

LGTM