Change ECHO extension description in manifest

BUG=chromium:331962
TEST=Tested manually on daisy

Review URL: https://codereview.chromium.org/120513008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248251 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 248251