[Files.app] Enable the suggest-an-app dialog by default.

Once it has been disabled in M31 since was decided as no-go in Chrome 31. This patch re-enabled the feature in ToT.

BUG=none
TEST=manual
R=hirono@chromium.org

Review URL: https://codereview.chromium.org/31813003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@231298 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 231298