[Downloads] Remove intermediate files when no longer necessary.

When cancelling or removing an interrupted download, the associated
intermediate file should also be removed. That file is only necessary if
the download is going to be resumed.

BUG=7648
BUG=196806

Review URL: https://chromiumcodereview.appspot.com/14958002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@201883 0039d316-1c4b-4281-b951-d872f2087c98
3 files changed