Reland r240054: Files.app: Show full error message of progress items.

Previous CL breaks the Transfer tests because the name of variable is wrong and
the code path to run the wrong line is executed.

Previously reverted CL: crrev.com/103803007

BUG=323194,327761
TEST=Make reproduce code to run the code path, file_manager_browser_tests

Review URL: https://codereview.chromium.org/106843003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@240674 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 240674