Settings Idle Load: Use templatize, add closure compiler target

- Use Polymer.Templatize instead of extending Templatizer behavior,
  since Templatizer behavior is now legacy/deprecated.
- Add a closure compiler target for settings idle load

This is in preparation for migrating settings idle load to Polymer 3

Bug: 1042558
Change-Id: I820f1a51aff09478277f3aae1ad1611fdc334a59
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2023472
Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#735746}

chrome/browser/resources/settings/controls/BUILD.gn

@@ -14,6 +14,7 @@ js_type_check("closure_compile") {
     ":settings_boolean_control_behavior",
     ":settings_checkbox",
     ":settings_dropdown_menu",
+    ":settings_idle_load",
     ":settings_radio_group",
     ":settings_slider",
     ":settings_textarea",
@@ -88,6 +89,10 @@ js_library("settings_dropdown_menu") {
   externs_list = [ "$externs_path/settings_private.js" ]
 }
 
+js_library("settings_idle_load") {
+  externs_list = [ "$externs_path/pending_polymer.js" ]
+}
+
 js_library("settings_radio_group") {
   deps = [
     ":pref_control_behavior",

chrome/browser/resources/settings/controls/settings_idle_load.js

@@ -11,8 +11,6 @@
 Polymer({
   is: 'settings-idle-load',
 
-  behaviors: [Polymer.Templatizer],
-
   properties: {
     /**
      * If specified, it will be loaded via an HTML import before stamping the
@@ -32,7 +30,9 @@ Polymer({
 
   /** @override */
   attached() {
-    this.idleCallback_ = requestIdleCallback(this.get.bind(this));
+    this.idleCallback_ = requestIdleCallback(() => {
+      this.get();
+    });
   },
 
   /** @override */
@@ -52,11 +52,14 @@ Polymer({
 
     this.loading_ = new Promise((resolve, reject) => {
       this.importHref(this.url, () => {
-        assert(!this.ctor);
-        this.templatize(this.getContentChildren()[0]);
-        assert(this.ctor);
-
-        this.instance_ = this.stamp({});
+        const template =
+            /** @type {!HTMLTemplateElement} */ (this.getContentChildren()[0]);
+        const TemplateClass = Polymer.Templatize.templatize(template, this, {
+          mutableData: false,
+          forwardHostProp: this._forwardHostPropV2,
+        });
+
+        this.instance_ = new TemplateClass();
 
         assert(!this.child_);
         this.child_ = this.instance_.root.firstElementChild;