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* Make StoreActiveEntryUniqueID() take no args -- the arg was unnecessary.
* Remove the unique ID setter and make its lone caller override ShouldExpireInternal() instead, to reduce the overall API surface area.
* Prefer to override ShouldExpireInternal() instead of ShouldExpire() where possible, as that's a safer pattern if others copy-and-paste it, since it will change less behavior.

BUG=none
TEST=none
Review URL: https://codereview.chromium.org/11748012

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@175362 0039d316-1c4b-4281-b951-d872f2087c98