Move EventListenerMap to src/extensions/browser/

This is a dependency of EventRouter, which is almost ready to move.

Also convert the unit test to use BrowserContext instead of Profile.

BUG=316367
TEST=unit_tests

Review URL: https://codereview.chromium.org/59823011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236190 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 236190