refactor: defer scroll position adjustment until rAF

src/vaadin-combo-box-mixin.html

@@ -548,8 +548,12 @@
 
       // Ensure metrics are up-to-date
       this.$.overlay.updateViewportBoundaries();
-      Polymer.Async.microTask.run(() => this.$.overlay.adjustScrollPosition());
+      // Force iron-list to create reusable nodes. Otherwise it will only start
+      // doing that in scroll listener, which is especially slow in Edge.
+      this.$.overlay._selector._increasePoolIfNeeded();
       setTimeout(() => this._resizeDropdown(), 1);
+      // Defer scroll position adjustment to prevent freeze in Edge
+      window.requestAnimationFrame(() => this.$.overlay.adjustScrollPosition());
 
 
       // _detectAndDispatchChange() should not consider value changes done before opening

test/.eslintrc.json

@@ -22,6 +22,7 @@
     "fire": false,
     "fireMousedownMouseupClick": false,
     "getCustomPropertyValue": false,
+    "onceScrolled": false,
     "System": false,
     "HTMLImports": false,
     "MockInteractions": false,

test/common.js

@@ -34,6 +34,18 @@ var fireMousedownMouseupClick = (node) => {
   fire('click', node);
 };
 
+var onceScrolled = (scroller) => {
+  return new Promise(resolve => {
+    const listener = () => {
+      scroller.removeEventListener('scroll', listener);
+      setTimeout(() => {
+        resolve();
+      });
+    };
+    scroller.addEventListener('scroll', listener);
+  });
+};
+
 var describeSkipIf = (bool, title, callback) => {
   bool = typeof bool == 'function' ? bool() : bool;
   if (bool) {

test/filtering.html

@@ -125,9 +125,11 @@
         setInputValue('b');
 
         // first scroll after open is async
-        setTimeout(() => {
-          expect(spy.callCount).to.eql(1); // scrolls once on open
-          done();
+        window.requestAnimationFrame(() => {
+          setTimeout(() => {
+            expect(spy.callCount).to.eql(1); // scrolls once on open
+            done();
+          }, 1);
         });
       });
 

test/keyboard.html

@@ -530,7 +530,7 @@
 
         comboBox.open();
 
-        setTimeout(() => {
+        onceScrolled(comboBox.$.overlay._scroller).then(() => {
           expect(selector.firstVisibleIndex).to.be.within(50 - comboBox.$.overlay._visibleItemsCount(), 50);
           done();
         });

test/scrolling.html

@@ -85,10 +85,10 @@
           combobox.value = combobox.items[50];
           combobox.open();
 
-          setTimeout(() => {
+          onceScrolled(combobox.$.overlay._scroller).then(() => {
             expectSelectedItemPositionToBeVisible();
             done();
-          }, 1);
+          });
         });
 
         it('should make selected item visible after reopen', done => {