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..3879b397f77bb1cd4a9543250d52f4ea0c7e4932 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 +67,34 @@ Polymer({
   /** @override */
   attached: function() {
     if (this.showScrollBorders) {
+      this.mutationObserver_ = new MutationObserver(function() {
+        if (this.open) {
+          this.addIntersectionObserver_();
+        } else {
+          this.removeIntersectionObserver_();
+        }
+      }.bind(this));
+
+      var observerConfig = {

[dpapad, 2017/04/13 20:31:39]

Nit (optional): Since this is only used once below, inline it instead?

[scottchen, 2017/04/13 21:46:04]

Done.

+        attributes: true,
+        attributeFilter: ['open'],
+      };
+
+      this.mutationObserver_.observe(this, observerConfig);
+    }
+  },
+
+  /** @override */
+  detached: function() {
+    if (this.mutationObserver_) {
+      this.mutationObserver_.disconnect();
+      this.mutationObserver_ = null;
+    }

[dpapad, 2017/04/13 20:31:39]

Previous code was removing the IntersectionObserver on detached, latest version
does not. For example say someone is calling dialog.remove() without having
called close() first. Would the IntersectionObserver leak?

[scottchen, 2017/04/13 21:46:04]

Yes, will leak. Fixed.

+  },
+
+  /** @private */
+  addIntersectionObserver_: function() {
+    if (!this.intersectionObserver_) {
       var bodyContainer = this.$$('.body-container');
 
       var bottomMarker = this.$.bodyBottomMarker;
@@ -89,13 +120,14 @@ Polymer({
             root: bodyContainer,
             threshold: 0,
           }));
+

[dpapad, 2017/04/13 20:31:39]

Nit (optional): Revert this?

[scottchen, 2017/04/13 21:46:04]

Done.

       this.intersectionObserver_.observe(bottomMarker);
       this.intersectionObserver_.observe(topMarker);
     }
   },
 
-  /** @override */
-  detached: function() {
+  /** @private */
+  removeIntersectionObserver_: function() {
     if (this.intersectionObserver_) {
       this.intersectionObserver_.disconnect();
       this.intersectionObserver_ = null;