MD History: update iron-list and dependencies for better scroll performance

chrome/test/data/webui/md_history/md_history_browsertest.js

Index: chrome/test/data/webui/md_history/md_history_browsertest.js
diff --git a/chrome/test/data/webui/md_history/md_history_browsertest.js b/chrome/test/data/webui/md_history/md_history_browsertest.js
index ee132c5ee98cec82084ab7b3565a29cfcd8cc50a..61777b5c0695f11a8334f024f6d30224209b204c 100644
--- a/chrome/test/data/webui/md_history/md_history_browsertest.js
+++ b/chrome/test/data/webui/md_history/md_history_browsertest.js
@@ -48,6 +48,16 @@ MaterialHistoryBrowserTest.prototype = {
     suiteSetup(function() {
       // Wait for the top-level app element to be upgraded.
       return waitForAppUpgrade()
+          .then(function() {
+            // <iron-list>#_maxPages controls the default number of "pages" of
+            // "physical" (i.e. DOM) elements to render. Some of these tests
+            // rely on rendering up to 3 "pages" of items, which was previously
+            // the default, changeed to 2 for performance reasons. TODO(dbeam):
+            // maybe trim down the number of items created in the tests? Or
+            // don't touch <iron-list>'s physical items as much?
+            Array.from(document.querySelectorAll('* /deep/ iron-list')).forEach(
+                function(ironList) { ironList._maxPages = 3; });
+          })
           .then(function() { return md_history.ensureLazyLoaded(); })
           .then(function() {
             $('history-app').queryState_.queryingDisabled = true;