Remove DISALLOW_ macro from libcef_dll/ (see issue #3234)

Also perform related C++ cleanup:
- Use =default instead of {} for default implementations of
  constructors/destructors.
- Replace typedef with using.

include/wrapper/cef_message_router.h

@@ -245,7 +245,7 @@ class CefMessageRouterBrowserSide
   ///
   class Handler {
    public:
-    typedef CefMessageRouterBrowserSide::Callback Callback;
+    using Callback = CefMessageRouterBrowserSide::Callback;
 
     ///
     // Executed when a new query is received. |query_id| uniquely identifies the