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This switches HistoryDatabase to composition, so the clients doesn't have to
depend/include starred_url_database.h anymore.

NOTE: This was a TODO for sky@.

R=sky@chromium.org

Review URL: http://codereview.chromium.org/8550006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@111179 0039d316-1c4b-4281-b951-d872f2087c98