Fix selection of download URLs
Fix selection of download URLs

In progress downloads would clear the selection of the url every time the
progress updates, making it impossible to copy a url.

BUG=44982
TEST=Download a large file, and select it's URL as it is downloading.  It should
stay selected.

Review URL: http://codereview.chromium.org/2966008

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@52267 0039d316-1c4b-4281-b951-d872f2087c98

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