Spellchecker should recheck after changing language.

This patch introduces a code to request spell checking after changing language.

In http://trac.webkit.org/changeset/105489, we have added a webkit interface to request spell checking from chromium. This patch calls the API when we the spellcheck language is changed.

BUG=21225
TEST=MANUAL

[shinyak, 2012-01-30 07:05:19]

Hi,

I've implemented a patch to recheck spelling when changing spellcheck language.
I think this patch is desired for long by multi-lingual users.

Currently Linux and Windows do not have implementation of asynchronous
spellchecking, you need the following patch for testing on their platforms
before it is landed.
http://codereview.chromium.org/9169082/

I would like bono-san to check this patch goes well.
And I would like Avi to give LGTM if bono-san doesn't complain the patch and Avi
thinks this patch OK.

[Avi (use Gerrit), 2012-02-01 15:48:00]

I'd like John to take a look at this. We've tended to keep spellchecking out of
content, but this WebKit patch seems to have already jumped that fence.

[jam, 2012-02-01 17:15:16]

On 2012/02/01 15:48:00, Avi wrote:
> I'd like John to take a look at this. We've tended to keep spellchecking out
of
> content, but this WebKit patch seems to have already jumped that fence.

thanks for checking. WebKit does have support for spellcheck because it needs
to, but content layer doesn't know about it. see WebSpellCheckClient.h which is
implemented by chrome code.

so this message should be defined in spellcheck_messages.h, sent directly from
spellchecker_submenu_observer_hunspell.cc, and handled in
spellcheck_provider.cc. That code can then call WebKit directly.

for general background about what's in content vs chrome, see
http://www.chromium.org/developers/content-module

[James Cook, 2012-02-01 18:13:31]

-jamescook.   I don't really know this code.

[jeremy, 2012-02-06 05:46:31]

This code should be #ifdef-ed out on OS X since it's only needed when using
Hunspell and not applicable for using the native OS X spellchecker (see comment
#49 on crbug.com/21225) .