MD Settings: Prevent <settings-languages> running init code after is detached.

chrome/browser/resources/settings/languages_page/languages.js

Index: chrome/browser/resources/settings/languages_page/languages.js
diff --git a/chrome/browser/resources/settings/languages_page/languages.js b/chrome/browser/resources/settings/languages_page/languages.js
index e713a9642280fe49613e9ef812ae238b7a5a628a..40d9eb021d8466609e68b61b6c0b6cf7abe29262 100644
--- a/chrome/browser/resources/settings/languages_page/languages.js
+++ b/chrome/browser/resources/settings/languages_page/languages.js
@@ -145,8 +145,11 @@ Polymer({
         'languages)',
   ],
 
+  /** @private {?Function} */
+  boundOnInputMethodChanged_: null,
+
   /** @override */
-  created: function() {
+  attached: function() {

[michaelpg, 2017/03/28 20:30:10]

Is there a way to do this without waiting for |attached|? I don't have data to
back this up, but I would expect this to have some (possibly miniscule)
performance impact since we have to wait for these round trips from Chrome
before displaying any language settings.

Maybe that means moving only the Promise.all().then() to attached().

     this.languageSettingsPrivate =
         settings.languageSettingsPrivateApiForTest ||
         /** @type {!LanguageSettingsPrivate} */(chrome.languageSettingsPrivate);
@@ -195,13 +198,29 @@ Polymer({
     }
 
     Promise.all(promises).then(function(results) {
+      if (!this.isConnected) {
+        // Return early if this element was detached from the DOM before this
+        // async callback executes (can happen during testing).
+        return;
+      }
+
       this.createModel_(results[1], results[2], results[3], results[4]);
       this.resolver_.resolve();
     }.bind(this));
 
     if (cr.isChromeOS) {
+      this.boundOnInputMethodChanged_ = this.onInputMethodChanged_.bind(this);
       this.inputMethodPrivate.onChanged.addListener(
-          this.onInputMethodChanged_.bind(this));
+          assert(this.boundOnInputMethodChanged_));
+    }
+  },
+
+  /** @override */
+  detached: function() {
+    if (cr.isChromeOS) {
+      this.inputMethodPrivate.onChanged.removeListener(
+          assert(this.boundOnInputMethodChanged_));
+      this.boundOnInputMethodChanged_ = null;
     }
   },