Deprecate the External Extension Install via Preferences file (Windows only). Use the Registry to externally install extensions instead.

BUG=41902

Review URL: https://codereview.chromium.org/138053004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245235 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 245235
Revert 245226 "Nukes MessageLoop::Dispatcher"

> Nukes MessageLoop::Dispatcher
> 
> There is no point in this typedef now that MessagePumpDispatcher is
> its own class.
> 
> BUG=none
> TEST=none
> R=ben@chromium.org, darin@chromium.org
> 
> Review URL: https://codereview.chromium.org/139593002

TBR=sky@chromium.org

Review URL: https://codereview.chromium.org/138433008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245239 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 245239