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/alloy/alloy_browser_host_impl.cc

@@ -99,6 +99,9 @@ class CefWidgetHostInterceptor
     render_widget_host_->AddObserver(this);
   }
 
+  CefWidgetHostInterceptor(const CefWidgetHostInterceptor&) = delete;
+  CefWidgetHostInterceptor& operator=(const CefWidgetHostInterceptor&) = delete;
+
   blink::mojom::WidgetHost* GetForwardingInterface() override { return impl_; }
 
   // WidgetHostInterceptorForTesting method:
@@ -122,8 +125,6 @@ class CefWidgetHostInterceptor
   AlloyBrowserHostImpl* const browser_;
   content::RenderWidgetHostImpl* const render_widget_host_;
   blink::mojom::WidgetHost* const impl_;
-
-  DISALLOW_COPY_AND_ASSIGN(CefWidgetHostInterceptor);
 };
 
 static constexpr base::TimeDelta kRecentlyAudibleTimeout = base::Seconds(2);