MD Settings: Allow deleting read-only content setting exceptions.

chrome/browser/resources/settings/site_settings/site_list.js

Index: chrome/browser/resources/settings/site_settings/site_list.js
diff --git a/chrome/browser/resources/settings/site_settings/site_list.js b/chrome/browser/resources/settings/site_settings/site_list.js
index 7765e36d08cbcab3489a2b7a9aeb1f3f86231df6..5f6a29c89eec2327844adea6c69fd473117cea54 100644
--- a/chrome/browser/resources/settings/site_settings/site_list.js
+++ b/chrome/browser/resources/settings/site_settings/site_list.js
@@ -62,7 +62,9 @@ Polymer({
      */
     sites: {
       type: Array,
-      value: function() { return []; },
+      value: function() {
+        return [];
+      },
     },
 
     /**
@@ -74,10 +76,10 @@ Polymer({
     },
 
     /**
-      * The type of category this widget is displaying data for. Normally
-      * either 'allow' or 'block', representing which sites are allowed or
-      * blocked respectively.
-      */
+     * The type of category this widget is displaying data for. Normally
+     * either 'allow' or 'block', representing which sites are allowed or
+     * blocked respectively.
+     */
     categorySubtype: {
       type: String,
       value: settings.INVALID_CATEGORY_SUBTYPE,
@@ -128,9 +130,7 @@ Polymer({
     },
   },
 
-  observers: [
-    'configureWidget_(category, categorySubtype)'
-  ],
+  observers: ['configureWidget_(category, categorySubtype)'],
 
   ready: function() {
     this.addWebUIListener('contentSettingSitePermissionChanged',
@@ -214,6 +214,17 @@ Polymer({
    * @return {boolean}
    * @private
    */
+  isResetButtonHidden_: function(source, readOnlyList) {
+    return this.isExceptionControlled_(source) || this.allSites ||
+        !readOnlyList;
+  },
+
+  /**
+   * @param {string} source Where the setting came from.
+   * @param {boolean} readOnlyList Whether the site exception list is read-only.
+   * @return {boolean}
+   * @private
+   */
   isActionMenuHidden_: function(source, readOnlyList) {
     return this.isExceptionControlled_(source) || this.allSites || readOnlyList;
   },
@@ -494,6 +505,17 @@ Polymer({
    * @param {!{model: !{item: !SiteException}}} e
    * @private
    */
+  onResetButtonTap_: function(e) {
+    // Trigger same logic as opening the menu and choosing the Reset item.
+    this.actionMenuSite_ = e.model.item;
+    this.onActionMenuActivate_(settings.PermissionValues.DEFAULT);
+    this.actionMenuSite_ = null;

[dschuyler, 2017/03/22 21:19:19]

Hmm, it looks like onActionMenuActivate_ is an event handler because the name
starts with "on", but it appears to only be used as a private function (and not
as an event handler -- maybe the name should be changed).

Your choice:

Could you do me the favor of adding a 
// TODO(dschuyler): Change onActionMenuActivate_() to take a actionMenuSite_ so
that it doesn't need to be set/reset like this.

or

Go ahead and change onActionMenuActivate_() to take a actionMenuSite_ so that it
doesn't need to be set/reset like this.

[tommycli, 2017/03/22 21:51:29]

Done. Based on your feedback, I refactored it a bit to make it more obvious.
Still room for more improvement, but this is a decent state I think.

+  },
+
+  /**
+   * @param {!{model: !{item: !SiteException}}} e
+   * @private
+   */
   onShowActionMenuTap_: function(e) {
     this.actionMenuSite_ = e.model.item;
     /** @type {!CrActionMenuElement} */ (