Re-enable browser_tests NaClExtensionTest.
These were recently disabled but appear to be working now,
so perhaps some NaCl issue caused this.

BUG=319892

Review URL: https://codereview.chromium.org/76913002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236583 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 236583