Don't show downloads from web intents picker in shelf

This CL adds a new attribute to DownloadItem that can be used to suppress the download shelf.

This attribute is set the by web intent picker to hide extension downloads.

BUG=152010
TBR=sky@chromium.org
TEST=Go to http://webintents.org. Click share. Click "Add to Chrome". Verify that the download shelf is not shown.

Review URL: https://chromiumcodereview.appspot.com/11016022

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@161040 0039d316-1c4b-4281-b951-d872f2087c98
5 files changed