Omnibox: Reduce Bolding Flicker in SearchProvider

This code extends the code from
https://codereview.chromium.org/23164011/
that prevents query suggestions from flipping highlighting state too
dramatically as the user types to prevent the analogous situation happening
to navigation suggestions.

The analogous situation is less obvious.  When query suggestions flip state,
they go from partially bolded to total bolded.  When navigation suggestions
flip state, they go from partially bolded to not bolded at all.  This is
probably still worth fixing, though it's much less significant.  On the
other hand, if you think the code is too complicated, then maybe we shouldn't
bother?

In particular, this change:
* Moves match_contents_ and match_contents_class_ from SuggestResult to
  the base class Result.
* Adds code to NavigationResult to populate these fields.  The majority of
  this code is a simple copy-paste or cut-paste from elsewhere in this
  file.  There's obviously some additional code here to deal with the
  parameter |allow_bolding_nothing|.
* Adds drops of code in various places to pass the user's accept language
  settings around, which are used to decide what and how to display URLs.
* Revises the appropriate call to UpdateMatchContentsClass().

For reference, an earlier tentative changelist fixed both query suggestions
and navigation suggestion at the same time.  If you care to look at it, it's
patchset 4 of https://codereview.chromium.org/23164011/#ps26001
(Or you can take my word that incorporate the comments from that
changelist as best as possible.)

BUG=259486

Review URL: https://codereview.chromium.org/134453003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245069 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 245069