Whitelist experimental extension for bookmarkManagerPrivate API.

Removes "component" restriction as this used to only be used by the
baked-in bookmark manager extension.
BUG=312900
R=kalman@chromium.org

Review URL: https://codereview.chromium.org/59223009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@234562 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 234562