Implement API to send navigator.qt message from host to client process.

This is still missing the interesting part, namely calling the
JavaScript navigator.qt.onmessage function.

Change-Id: Iaac0177e096f02e02b6c23ad6ea9326a1819b563
Use strict comparison operators in JavaScript navigator.qt API.

Change-Id: I63c0101473a1e7a109a364d9b083cf79dc6d465c
Basic implementation of navigator.qt.onmessage JS to C++ connection.

This connects the JavaScript API to native C++ code. What is missing
is the actual implementation of the C++ code.

Change-Id: I512446059e68aeaf6434b68d69303d9c860365d1