Refactor the ViewHistory to utilize async methods rather than man…

…ually returning `Promise`s

web/view_history.js

@@ -54,64 +54,54 @@ class ViewHistory {
     });
   }
 
-  _writeToStorage() {
-    return new Promise((resolve) => {
-      let databaseStr = JSON.stringify(this.database);
+  async _writeToStorage() {
+    let databaseStr = JSON.stringify(this.database);
 
-      if (typeof PDFJSDev !== 'undefined' &&
-          PDFJSDev.test('FIREFOX || MOZCENTRAL')) {
-        sessionStorage.setItem('pdfjs.history', databaseStr);
-      } else {
-        localStorage.setItem('pdfjs.history', databaseStr);
-      }
-      resolve();
-    });
+    if (typeof PDFJSDev !== 'undefined' &&
+        PDFJSDev.test('FIREFOX || MOZCENTRAL')) {
+      sessionStorage.setItem('pdfjs.history', databaseStr);
+      return;
+    }
+    localStorage.setItem('pdfjs.history', databaseStr);
   }
 
-  _readFromStorage() {
-    return new Promise(function(resolve) {
-      if (typeof PDFJSDev !== 'undefined' &&
-          PDFJSDev.test('FIREFOX || MOZCENTRAL')) {
-        resolve(sessionStorage.getItem('pdfjs.history'));
-      } else {
-        resolve(localStorage.getItem('pdfjs.history'));
-      }
-    });
+  async _readFromStorage() {
+    if (typeof PDFJSDev !== 'undefined' &&
+        PDFJSDev.test('FIREFOX || MOZCENTRAL')) {
+      return sessionStorage.getItem('pdfjs.history');
+    }
+    return localStorage.getItem('pdfjs.history');
   }
 
-  set(name, val) {
-    return this._initializedPromise.then(() => {
-      this.file[name] = val;
-      return this._writeToStorage();
-    });
+  async set(name, val) {
+    await this._initializedPromise;
+    this.file[name] = val;
+    return this._writeToStorage();
   }
 
-  setMultiple(properties) {
-    return this._initializedPromise.then(() => {
-      for (let name in properties) {
-        this.file[name] = properties[name];
-      }
-      return this._writeToStorage();
-    });
+  async setMultiple(properties) {
+    await this._initializedPromise;
+    for (let name in properties) {
+      this.file[name] = properties[name];
+    }
+    return this._writeToStorage();
   }
 
-  get(name, defaultValue) {
-    return this._initializedPromise.then(() => {
-      let val = this.file[name];
-      return val !== undefined ? val : defaultValue;
-    });
+  async get(name, defaultValue) {
+    await this._initializedPromise;
+    let val = this.file[name];
+    return val !== undefined ? val : defaultValue;
   }
 
-  getMultiple(properties) {
-    return this._initializedPromise.then(() => {
-      let values = Object.create(null);
+  async getMultiple(properties) {
+    await this._initializedPromise;
+    let values = Object.create(null);
 
-      for (let name in properties) {
-        let val = this.file[name];
-        values[name] = val !== undefined ? val : properties[name];
-      }
-      return values;
-    });
+    for (let name in properties) {
+      let val = this.file[name];
+      values[name] = val !== undefined ? val : properties[name];
+    }
+    return values;
   }
 }