Fix spurious error messages when updating contextual menu

There were spurious error messages in the dev console of
uBO in Firefox, because Firefox does not silently ignore
duplicate contextual menu entries, which could occur
transiently when the contextual menu entries were updated.

The fix simplifies contextual menu code, and actually
fulfill the original goal of avoiding to call extensions
framework API as much as possible.

platform/chromium/vapi-background.js

@@ -1415,35 +1415,20 @@ vAPI.Net = class {
 
 vAPI.contextMenu = webext.menus && {
     _callback: null,
-    _entries: [],
-    _createEntry: function(entry) {
-        webext.menus.create(JSON.parse(JSON.stringify(entry)));
-    },
+    _hash: '',
     onMustUpdate: function() {},
     setEntries: function(entries, callback) {
         entries = entries || [];
-        let n = Math.max(this._entries.length, entries.length);
-        for ( let i = 0; i < n; i++ ) {
-            const oldEntryId = this._entries[i];
-            const newEntry = entries[i];
-            if ( oldEntryId && newEntry ) {
-                if ( newEntry.id !== oldEntryId ) {
-                    webext.menus.remove(oldEntryId);
-                    this._createEntry(newEntry);
-                    this._entries[i] = newEntry.id;
-                }
-            } else if ( oldEntryId && !newEntry ) {
-                webext.menus.remove(oldEntryId);
-            } else if ( !oldEntryId && newEntry ) {
-                this._createEntry(newEntry);
-                this._entries[i] = newEntry.id;
-            }
-        }
-        n = this._entries.length = entries.length;
+        const hash = entries.map(v => v.id).join();
+        if ( hash === this._hash ) { return; }
+        this._hash = hash;
+        webext.menus.removeAll();
+        for ( const entry of entries ) {
+            webext.menus.create(JSON.parse(JSON.stringify(entry)));
+        }
+        const n = entries.length;
         callback = callback || null;
-        if ( callback === this._callback ) {
-            return;
-        }
+        if ( callback === this._callback ) { return; }
         if ( n !== 0 && callback !== null ) {
             webext.menus.onClicked.addListener(callback);
             this._callback = callback;

platform/chromium/webext.js

@@ -73,6 +73,7 @@ const webext = {
         },
         onClicked: chrome.contextMenus.onClicked,
         remove: promisifyNoFail(chrome.contextMenus, 'remove'),
+        removeAll: promisifyNoFail(chrome.contextMenus, 'removeAll'),
     },
     // https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/privacy
     privacy: {