MD Settings: in cr_dialog, prevent intersectionObserver from firing early.

ui/webui/resources/cr_elements/cr_dialog/cr_dialog.js

 // Copyright 2016 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.
 
 /**
  * @fileoverview 'cr-dialog' is a component for showing a modal dialog. If the
  * dialog is closed via close(), a 'close' event is fired. If the dialog is
  * canceled via cancel(), a 'cancel' event is fired followed by a 'close' event.
  * Additionally clients can inspect the dialog's |returnValue| property inside
  * the 'close' event listener to determine whether it was canceled or just
@@ skipping 65 matching lines @@
           assert(target == bottomMarker || target == topMarker);
 
           var classToToggle =
               target == bottomMarker ? 'bottom-scrollable' : 'top-scrollable';
 
           bodyContainer.classList.toggle(
               classToToggle, entries[i].intersectionRatio == 0);
         }
       };
 
       this.intersectionObserver_ = new IntersectionObserver(

[Dan Beam, 2017/04/12 01:09:43]

note: you might want to do this inside of your afterNextRender() as well as
check whether this.isAttached in the afterNextRender callback

[scottchen, 2017/04/12 01:43:05]

Done. Also moved the contained code to a separate method, nesting gettin' real.

           callback,
           /** @type {IntersectionObserverInit} */ ({
             root: bodyContainer,
             threshold: 0,
           }));
-      this.intersectionObserver_.observe(bottomMarker);
-      this.intersectionObserver_.observe(topMarker);
+
+      // Make sure the handler isn't triggered before the dialog is rendered.
+      Polymer.RenderStatus.afterNextRender(this, function() {

[dpapad, 2017/04/12 01:05:51]

Should we be calling observe() in ready() instead? According to the docs
"Called after property values are set and local DOM is initialized."

[Dan Beam, 2017/04/12 01:07:13]

i'm fairly sure that attached() happens after ready().

[scottchen, 2017/04/12 01:43:05]

Yep, attached() fires after ready(). Not sure if it's due to how dialog gets
rendered, but apparently when attached() gets called, only the overlay is
visible, the actual modal is not yet.

+        this.intersectionObserver_.observe(bottomMarker);
+        this.intersectionObserver_.observe(topMarker);
+      });
     }
   },
 
   /** @override */
   detached: function() {
     if (this.intersectionObserver_) {
       this.intersectionObserver_.disconnect();
       this.intersectionObserver_ = null;
     }
   },
@@ skipping 29 matching lines @@
       return;
 
     var actionButton =
         this.querySelector('.action-button:not([disabled]):not([hidden])');
     if (actionButton) {
       actionButton.click();
       e.preventDefault();
     }
   },
 });