Neutralize `localStorage` access on mobile platform

Related issue:
- https://github.com/uBlockOrigin/uBlock-issues/issues/899

window.localStorage is synchronous and thus should be
avoided at launch time. Currently the avoidance is only
for mobile platforms.

platform/chromium/vapi-background.js

@@ -1443,7 +1443,14 @@ vAPI.cloud = (( ) => {
 
     const options = {
         defaultDeviceName: window.navigator.platform,
-        deviceName: vAPI.localStorage.getItem('deviceName') || ''
+        deviceName: undefined,
+    };
+
+    const getDeviceName = function() {
+        if ( options.deviceName === undefined ) {
+            options.deviceName = vAPI.localStorage.getItem('deviceName') || '';
+        }
+        return options.deviceName;
     };
 
     // This is used to find out a rough count of how many chunks exists:
@@ -1491,9 +1498,8 @@ vAPI.cloud = (( ) => {
     };
 
     const push = async function(dataKey, data) {
-
         let bin = {
-            'source': options.deviceName || options.defaultDeviceName,
+            'source': getDeviceName() || options.defaultDeviceName,
             'tstamp': Date.now(),
             'data': data,
             'size': 0
@@ -1579,6 +1585,7 @@ vAPI.cloud = (( ) => {
 
     const getOptions = function(callback) {
         if ( typeof callback !== 'function' ) { return; }
+        getDeviceName();
         callback(options);
     };
 

platform/chromium/vapi-common.js

@@ -226,6 +226,10 @@ vAPI.closePopup = function() {
 //   Always use a wrapper to seamlessly handle exceptions
 
 vAPI.localStorage = {
+    started: vAPI.webextFlavor.soup.has('mobile') === false,
+    start: function() {
+        this.started = true;
+    },
     clear: function() {
         try {
             window.localStorage.clear();
@@ -233,6 +237,7 @@ vAPI.localStorage = {
         }
     },
     getItem: function(key) {
+        if ( this.started === false ) { return null; }
         try {
             return window.localStorage.getItem(key);
         } catch(ex) {
@@ -246,6 +251,7 @@ vAPI.localStorage = {
         }
     },
     setItem: function(key, value) {
+        if ( this.started === false ) { return; }
         try {
             window.localStorage.setItem(key, value);
         } catch(ex) {

src/js/start.js

@@ -316,6 +316,10 @@ if ( selfieIsValid !== true ) {
 // Start network observers.
 µb.webRequest.start();
 
+// https://github.com/uBlockOrigin/uBlock-issues/issues/899
+//   Signal that localStorage can be used now that uBO is ready.
+vAPI.localStorage.start();
+
 // Ensure that the resources allocated for decompression purpose (likely
 // large buffers) are garbage-collectable immediately after launch.
 // Otherwise I have observed that it may take quite a while before the