Update thumbnail_database to store times using ToInternalValue()

Update thumbnail_database to store times using ToInternalValue().
Modify ThumbnailScore::Equals() to test whether the time_at_snapshot match exactly.

BUG=None
Test=ThumbnailDatabaseTest.* ThumbnailScoreTest.* pass

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=155037

[pkotwicz, 2012-09-05 16:22:11]

Updated thumbnail_database to store last updated times for favicons and
thumbnails in microsends using ToInternalValue().
It is expected that this patch will expire all favicons and make thumbnails
super boring.

Mazda can you look at the Thumbnail related change? In particular do you know of
any other places which would be constructing a ThumbnailScore with a low res
time? (I couldn't find any)

[sky, 2012-09-05 16:57:17]

The code in thumbnaildb for topsites isn't really used anymore. It's in
topsitesdb now and it convertes to internal value.

[sky, 2012-09-05 16:57:20]

LGTM

[mazda, 2012-09-05 17:03:57]

lgtm

I don't think thumbnail score with a low res time is used in any other places as
far as I know.

[commit-bot: I haz the power, 2012-09-05 20:45:18]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/pkotwicz@chromium.org/10915092/2001

[commit-bot: I haz the power, 2012-09-05 22:33:19]

Change committed as 155037