Revert 175871

Revert 175871
This change didn't end up being the source of the ChromeOS problems so I'm
reverting my revert.

> Revert 175826
> 
> This change appears to be breaking the ChromeOS(x86) and ChromeOS(amd64) bots.
> http://build.chromium.org/p/chromium.chromiumos/builders/ChromiumOS%20%28x86%29/builds/11010
> 
> > Clean up: remove unnecessary if-branches on initialization of the a11y prefs.
> > 
> > According to the comment at preferences.cc:96, some accessibility prefs may be already registered in WizardController::RegisterPrefs. But the magnifier prefs are never registered there, hence we can remove if statements.
> > 
> > BUG=none
> > TEST=launch ChromeOS, and login.
> > 
> > Review URL: https://chromiumcodereview.appspot.com/11820018
> 
> TBR=yoshiki@chromium.org
> Review URL: https://codereview.chromium.org/11817029

TBR=acolwell@chromium.org
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=175937