Wrap GeminiScrollbar in a component, enabled forceGemini

Fixes https://github.com/vector-im/riot-web/issues/6294

src/components/views/elements/GeminiScrollbarWrapper.js

@@ -0,0 +1,36 @@
+/*
+Copyright 2018 New Vector Ltd.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import React from 'react';
+import GeminiScrollbar from 'react-gemini-scrollbar';
+
+class GeminiScrollbarWrapper extends React.Component {
+    render() {
+        // Enable forceGemini so that gemini is always enabled. This is
+        // to avoid future issues where a feature is implemented without
+        // doing QA on every OS/browser combination.
+        //
+        // By default GeminiScrollbar allows native scrollbars to be used
+        // on macOS. Use forceGemini to enable Gemini's non-native
+        // scrollbars on all OSs.
+        return <GeminiScrollbar forceGemini={true} {...this.props}>
+            { this.props.children }
+        </GeminiScrollbar>;
+    }
+}
+
+export default GeminiScrollbarWrapper;
+