DEV: polyfill Object.values and use where needed

We now have polyfills for `values` IE and `entries` IE

This commit uses values where appropriate to eliminate an extra lookup
This simplifies the code a bit.

Followup to: 7f089f07a7

app/assets/javascripts/discourse/components/composer-editor.js.es6

@@ -526,9 +526,7 @@ export default Ember.Component.extend({
       post.set("refreshedPost", true);
     }
 
-    Object.keys(oneboxes).forEach(oneboxURL => {
-      const onebox = oneboxes[oneboxURL];
-
+    Object.values(oneboxes).forEach(onebox => {
       onebox.forEach($onebox => {
         load({
           elem: $onebox,

app/assets/javascripts/discourse/components/scrolling-post-stream.js.es6

@@ -252,7 +252,7 @@ export default MountWidget.extend({
       uncloak(post, this);
     });
 
-    Object.keys(prev).forEach(pn => cloak(prev[pn], this));
+    Object.values(prev).forEach(node => cloak(node, this));
 
     this._previouslyNearby = newPrev;
     this.screenTrack.setOnscreen(onscreenPostNumbers);

app/assets/javascripts/discourse/models/topic-tracking-state.js.es6

@@ -373,8 +373,7 @@ const TopicTrackingState = Discourse.Model.extend({
 
   countCategory(category_id) {
     let sum = 0;
-    Object.keys(this.states).forEach(topicState => {
-      const topic = this.states[topicState];
+    Object.values(this.states).forEach(topic => {
       if (topic.category_id === category_id && !topic.deleted) {
         sum +=
           topic.last_read_post_number === null ||

app/assets/javascripts/discourse/widgets/post-menu.js.es6

@@ -404,8 +404,7 @@ export default createWidget("post-menu", {
       ])
     );
 
-    Object.keys(_extraButtons).forEach(k => {
-      const builder = _extraButtons[k];
+    Object.values(_extraButtons).forEach(builder => {
       if (builder) {
         const buttonAtts = builder(attrs, this.state, this.siteSettings);
         if (buttonAtts) {

app/assets/javascripts/polyfills.js

@@ -10,6 +10,19 @@ if (!Object.entries) {
   };
 }
 
+// adapted from https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/entries
+// missing in ie only
+if (!Object.values) {
+  Object.values = function(obj) {
+    var ownProps = Object.keys(obj),
+      i = ownProps.length,
+      resArray = new Array(i); // preallocate the Array
+    while (i--) resArray[i] = obj[ownProps[i]];
+
+    return resArray;
+  };
+}
+
 // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign
 if (typeof Object.assign !== "function") {
   // Must be writable: true, enumerable: false, configurable: true