Use no-break space for "Learn more" string to discourage line-break.

For example, we use "Learn more" string on Android Geolocation infobar.
Use no-break space instead of normal space to prevent line-break between
the two words.

Note that other places also use IDS_LEARN_MORE, but should be fine.

NOTRY=true
BUG=298445

Review URL: https://codereview.chromium.org/25920004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227969 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 227969