Update web extension to check for errors when invoking page state
methods and pass a message back if found. Check for this, decode and
throw a vala error in the WebView if found.
Use WebKitGTK UserMessage objects for invoking JS methods rather than
serialising to JS strings and running those. This is possibly slightly
less efficient, but removes the onus on serialising to and parsing from
JS and once switched over from message handlers to UserMessage objects
will be using a single uniform IPC interface for both.
Revert merge request GNOME/geary!374 for now since the shared process
model breaks old-style WebProcess message handler IPC.
This can be un-reverted when out JS is ported to the new Messages API
that is landing in WebKitGTK 2.28.
This reverts commit e4a5b85698, reversing
changes made to 66f6525480.
