[Downloads] Ask DownloadHistory if a download was from history.

Observers of downloads currently assume that any download that is
created in the IN_PROGRESS state must be a new download, while all
others were restored from history. Pending changes to how downloads are
created in response to failed requests will mean that this assumption
will no longer hold.

This CL adds a WasRestoredFromHistory() method to DownloadHistory which
determines whether a given download was restored from history.

BUG=7648

Review URL: https://codereview.chromium.org/230103002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@270749 0039d316-1c4b-4281-b951-d872f2087c98
11 files changed