Replaced ifvisible.js with simple drop-in to handle prefetch messages

dev/Common/Enums.js

@@ -460,7 +460,6 @@ export const ContactPropertyType = {
  */
 export const Magics = {
 	'EventWhichMouseMiddle': 3,
-	'ifvisibleIdle10s': 10,
 
 	'BitLength2048': 2048,
 	'BitLength1024': 1024,

dev/External/ifvisible.js

@@ -0,0 +1,46 @@
+(() => {
+    const doc = document,
+      visible = "visible",
+      wakeUp = () => {
+        clearTimeout(timer);
+        if (status !== visible) {
+          status = visible;
+        }
+        timer = setTimeout(() => {
+          if (status === visible) {
+            status = "idle";
+            dispatchEvent(new CustomEvent("idle"));
+          }
+        }, 10000);
+      };
+    var initialized = false,
+        status = visible,
+        timer = false;
+
+    function init() {
+      if (initialized) {
+        return true;
+      }
+      doc.addEventListener("visibilitychange", () => {
+        status = doc.visibilityState;
+        doc.hidden || wakeUp();
+      }, false);
+      initialized = true;
+      wakeUp();
+      doc.addEventListener("mousemove", wakeUp);
+      doc.addEventListener("keyup", wakeUp);
+      doc.addEventListener("touchstart", wakeUp);
+      addEventListener("scroll", wakeUp);
+    }
+
+    window.ifvisible = {
+      idle: callback => {
+        init();
+        addEventListener("idle", callback);
+      },
+      now: () => {
+        init();
+        return status === visible;
+      }
+    };
+})();