Remove unused reference to DownloadManager in PluginInstaller

BUG=237871
TEST=chrome compiles

Review URL: https://chromiumcodereview.appspot.com/15467002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@201092 0039d316-1c4b-4281-b951-d872f2087c98
2 files changed