[MD History] Force history results to be processed in order.

chrome/browser/resources/md_history/history.js

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Send the history query immediately. This allows the query to process during
 // the initial page startup.
 chrome.send('queryHistory', ['', 0, 0, 0, RESULTS_PER_PAGE]);
 chrome.send('getForeignSessions');
 
+/** @type {Promise} */
+var upgradePromise = null;
+
 /**
- * @param {HTMLElement} element
- * @return {!Promise} Resolves once a Polymer element has been fully upgraded.
+ * @return {!Promise} Resolves once the history-app has been fully upgraded.
  */
-function waitForUpgrade(element) {
-  return new Promise(function(resolve, reject) {
-    if (window.Polymer && Polymer.isInstance && Polymer.isInstance(element))
-      resolve();
-    else
-      $('bundle').addEventListener('load', resolve);
-  });
+function waitForAppUpgrade() {
+  if (!upgradePromise) {
+    upgradePromise = new Promise(function(resolve, reject) {
+      if (window.Polymer && Polymer.isInstance &&
+          Polymer.isInstance($('history-app'))) {
+        resolve();
+      } else {
+        $('bundle').addEventListener('load', resolve);
+      }
+    });
+  }
+  return upgradePromise;
 }
 
 // Chrome Callbacks-------------------------------------------------------------
 
 /**
  * Our history system calls this function with results from searches.
  * @param {HistoryQuery} info An object containing information about the query.
  * @param {!Array<HistoryEntry>} results A list of results.
  */
 function historyResult(info, results) {
-  var appElem = $('history-app');
-  waitForUpgrade(appElem).then(function() {
-    /** @type {HistoryAppElement} */(appElem).historyResult(info, results);
+  waitForAppUpgrade().then(function() {
+    /** @type {HistoryAppElement} */($('history-app'))
+        .historyResult(info, results);
     // TODO(tsergeant): Showing everything as soon as the list is ready is not
     // ideal, as the sidebar can still pop in after. Fix this to show everything
     // at once.
     document.body.classList.remove('loading');
   });
 }
 
 /**
  * Called by the history backend after receiving results and after discovering
  * the existence of other forms of browsing history.
  * @param {boolean} hasSyncedResults Whether there are synced results.
  * @param {boolean} includeOtherFormsOfBrowsingHistory Whether to include
  *     a sentence about the existence of other forms of browsing history.
  */
 function showNotification(
     hasSyncedResults, includeOtherFormsOfBrowsingHistory) {
   // TODO(msramek): |hasSyncedResults| was used in the old WebUI to show
   // the message about other signed-in devices. This message does not exist
   // in the MD history anymore, so the parameter is not needed. Remove it
   // when WebUI is removed and this becomes the only client of
   // BrowsingHistoryHandler.
-  var appElem = $('history-app');
-  waitForUpgrade(appElem).then(function() {
-    /** @type {HistoryAppElement} */(appElem)
+  waitForAppUpgrade().then(function() {
+    /** @type {HistoryAppElement} */($('history-app'))
         .getSideBar().showFooter = includeOtherFormsOfBrowsingHistory;
   });
 }
 
 /**
  * Receives the synced history data. An empty list means that either there are
  * no foreign sessions, or tab sync is disabled for this profile.
  * |isTabSyncEnabled| makes it possible to distinguish between the cases.
  *
  * @param {!Array<!ForeignSession>} sessionList Array of objects describing the
  *     sessions from other devices.
  * @param {boolean} isTabSyncEnabled Is tab sync enabled for this profile?
  */
 function setForeignSessions(sessionList, isTabSyncEnabled) {
-  var appElem = $('history-app');
-  waitForUpgrade(appElem).then(function() {
-    /** @type {HistoryAppElement} */(appElem)
+  waitForAppUpgrade().then(function() {
+    /** @type {HistoryAppElement} */($('history-app'))
         .setForeignSessions(sessionList, isTabSyncEnabled);
   });
 }
 
 /**
  * Called when the history is deleted by someone else.
  */
 function historyDeleted() {
 }
 
 /**
  * Called by the history backend after user's sign in state changes.
  * @param {boolean} isUserSignedIn Whether user is signed in or not now.
  */
 function updateSignInState(isUserSignedIn) {
-  var appElem = $('history-app');
-  waitForUpgrade(appElem).then(function() {
-    /** @type {HistoryAppElement} */(appElem)
+  waitForAppUpgrade().then(function() {
+    /** @type {HistoryAppElement} */($('history-app'))
         .updateSignInState(isUserSignedIn);
   });
 }