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

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

libcef/browser/views/display_impl.cc

@@ -45,7 +45,7 @@ void CefDisplay::GetAllDisplays(std::vector<CefRefPtr<CefDisplay>>& displays) {
 
   displays.clear();
 
-  typedef std::vector<display::Display> DisplayVector;
+  using DisplayVector = std::vector<display::Display>;
   DisplayVector vec = display::Screen::GetScreen()->GetAllDisplays();
   for (size_t i = 0; i < vec.size(); ++i)
     displays.push_back(new CefDisplayImpl(vec[i]));