Revert 58196 - GTTF: Clean up DownloadFileManager...

Revert 58196 - GTTF: Clean up DownloadFileManager

This removes a lot of duplication, locking, and thread jumping.

Most of the operations run on the FILE thread, and we do not duplicate
so much information. Each DownloadFile keeps track of its DownloadManager
(each Profile has its own DownloadManager). This allows us to remove
many maps from DownloadFileManager that were duplicating that information.

There is still SaveFileManager, but hopefully I will be able
to merge those two in small steps.

TEST=unit_tests, browser_tests, ui_tests
BUG=48913
Review URL: http://codereview.chromium.org/3245005

TBR=phajdan.jr@chromium.org

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=58718