Revert 102126 - Make cancel remove cancelled download from active queues at time of cancel.

Revert 102126 - Make cancel remove cancelled download from active queues at time of cancel.
Also add various tests required or enabled by this change.

This changes two aspects of Cancel semantics (for downloads, not save page):
a) Cancel can now be called anytime during the lifetime of a download, and
b) if it is called before the history callback occurs, the download will be removed from the system (no where to store it persistently while waiting)

BUG=85408
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=101510

Review URL: http://codereview.chromium.org/7796014

TBR=rdsmith@chromium.org
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=102136