Clear webFrame cache at a certain interval

mattermost-webapp is SPA. So cache is not cleared due to no navigation.
We needed to manually clear cache to free memory in long-term-use.

src/browser/webview/mattermost.js

@@ -7,6 +7,7 @@ const webFrame = electron.webFrame;
 const EnhancedNotification = require('../js/notification');
 
 const UNREAD_COUNT_INTERVAL = 1000;
+const CLEAR_CACHE_INTERVAL = 60 * 60 * 1000; // 1 hour
 
 Notification = EnhancedNotification; // eslint-disable-line no-global-assign, no-native-reassign
 
@@ -185,3 +186,10 @@ function setSpellChecker() {
 }
 setSpellChecker();
 ipc.on('set-spellcheker', setSpellChecker);
+
+// mattermost-webapp is SPA. So cache is not cleared due to no navigation.
+// We needed to manually clear cache to free memory in long-term-use.
+// http://seenaburns.com/debugging-electron-memory-usage/
+setInterval(() => {
+  webFrame.clearCache();
+}, CLEAR_CACHE_INTERVAL);