Movee EventConverter construction to EventFactoryWayland.
Migrate to use XKB Keyboard Layout implementation in Chromium.

So far, we handled key board event conversions ourselves. This patch
changes it to use upstream implementation, which removes lot of redundant
code.
Missing changes in Chromium.

This patch adds needed changes in Chromium for us to take use of the
upstream XKB keyboard implementation.
Converter: Use WeakPtrFactory for callbacks.

We currently post tasks in EventConverter which can outlive the instance of
that class. This patch changes so that we use WeakPtrFactory and ensure we
don't handle any callbacks once that instance is destroyed.