chromium: Disable "hotwording" by default.

There has been some recent news about that component extension on hacker
news:

https://news.ycombinator.com/item?id=9724409

Even though on our side it won't work, because we don't have NaCl
enabled by default or even working (I honestly haven't tested if it even
builds if enabled), we might get to the point where we can build with
NaCl enabled.

But until and even after that day, we want to have explicit control on
whether this extension is enabled.

Please also have a look at these two issues explaining the details
(about component extensions and the hotwording extension in particular):

https://crbug.com/491435
https://crbug.com/500922



Fixes issue #8358.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>