Enable navigator content utils by default

NavigatorContentUtils feature was added without any status, because it was already shipped
on some platforms. When applying a runtime flag to the feature, it is not enabled by default
because it doesn't have any status. So, we need to enable the NavigatorContentUtils by default,
because it was already shipped on some platforms.

BUG=N/A

Review URL: https://codereview.chromium.org/121643002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243026 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 243026