Revert 60378 (trying to track down http://crbug.com/56752 )- Flesh out URLLoa...

Revert 60378 (trying to track down http://crbug.com/56752 )- Flesh out URLLoader's download_to_file function.
* tie the lifetime of the resulting temp file to the lifetime of the URLLoader
  (the plan is to later extend the lifetime of the temp file to support xhr.responseBlob)
* make it work in test_shell
* make it work for sync requests
* added OnDataDownloaded messages to report progress

A related BlobURL loading change.
* grab a reference to the blob early on to ensure it's still there when the 'job' is finally started.

TEST=manual and deletable_file_reference_unittest.cc
BUG=52486
Review URL: http://codereview.chromium.org/3165062

TBR=michaeln@chromium.org

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=60425