appId service and removed unnecessary permissions from manifest

src/services/appIdService.js

@@ -0,0 +1,44 @@
+function AppIdService() {
+    initAppIdService();
+};
+
+function initAppIdService() {
+    AppIdService.prototype.getAppId = function (callback) {
+        if (!callback || typeof callback !== 'function') {
+            throw 'callback function required';
+        }
+
+        makeAndGetAppId('appId');
+    };
+
+    AppIdService.prototype.getAnonymousAppId = function (callback) {
+        if (!callback || typeof callback !== 'function') {
+            throw 'callback function required';
+        }
+
+        makeAndGetAppId('anonymousAppId');
+    };
+
+    function makeAndGetAppId(key) {
+        chrome.storage.local.get(key, function (obj) {
+            if (obj && obj[key]) {
+                callback(obj[key]);
+                return;
+            }
+
+            var setObj = {};
+            setObj[key] = newGuid();
+            chrome.storage.local.set(setObj, function () {
+                callback(setObj[key]);
+            });
+        });
+    }
+
+    // ref: http://stackoverflow.com/a/2117523/1090359
+    function newGuid() {
+        return 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, function (c) {
+            var r = Math.random() * 16 | 0, v = c === 'x' ? r : (r & 0x3 | 0x8);
+            return v.toString(16);
+        });
+    }
+};