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

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

Index: ui/webui/resources/cr_elements/cr_dialog/cr_dialog.js
diff --git a/ui/webui/resources/cr_elements/cr_dialog/cr_dialog.js b/ui/webui/resources/cr_elements/cr_dialog/cr_dialog.js
index c98c75ac4053eda397cdc7758103f9edb91fd87d..a1fdd7386168484f5bd81d91ff0839be8b50e0fc 100644
--- a/ui/webui/resources/cr_elements/cr_dialog/cr_dialog.js
+++ b/ui/webui/resources/cr_elements/cr_dialog/cr_dialog.js
@@ -48,6 +48,9 @@ Polymer({
   /** @private {?IntersectionObserver} */
   intersectionObserver_: null,
 
+  /** @private {?MutationObserver} */
+  mutationObserver_: null,
+
   /** @override */
   ready: function() {
     // If the active history entry changes (i.e. user clicks back button),
@@ -64,6 +67,33 @@ Polymer({
   /** @override */
   attached: function() {
     if (this.showScrollBorders) {
+      this.mutationObserver_ = new MutationObserver(function() {
+        if (this.open) {
+          this.addIntersectionObserver_();
+        } else {
+          this.removeIntersectionObserver_();
+        }
+      }.bind(this));
+
+      this.mutationObserver_.observe(this, {
+        attributes: true,
+        attributeFilter: ['open'],
+      });
+    }
+  },
+
+  /** @override */
+  detached: function() {
+    this.removeIntersectionObserver_();
+    if (this.mutationObserver_) {
+      this.mutationObserver_.disconnect();
+      this.mutationObserver_ = null;
+    }
+  },
+
+  /** @private */
+  addIntersectionObserver_: function() {

[dpapad, 2017/04/13 22:02:03]

Nit: You can reduce indentation throughout this method as follows

if (this.intersectionObserver)
  return;

// do stuff here....

[scottchen, 2017/04/13 22:33:29]

Done.

+    if (!this.intersectionObserver_) {
       var bodyContainer = this.$$('.body-container');
 
       var bottomMarker = this.$.bodyBottomMarker;
@@ -94,8 +124,8 @@ Polymer({
     }
   },
 
-  /** @override */
-  detached: function() {
+  /** @private */
+  removeIntersectionObserver_: function() {
     if (this.intersectionObserver_) {
       this.intersectionObserver_.disconnect();
       this.intersectionObserver_ = null;