Created attachment 177280 [details] [review]
Should I insert the elements in summaryItems[] grouped reflecting how the tray appears as well?

Tell me if this is complete. :)

Review of attachment 177280 [details] [review]:

The patch looks good and works as expected. Just a few cosmetic changes suggested below.

Commit message suggestion:
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Group chat sources on the left in the message tray

This will make it easier for users to get back to their chats.
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It doesn't appear to be important to preserve the same order when adding the elements to this._summaryItems , but it's great that you thought of that :).

::: js/ui/messageTray.js
@@ +990,3 @@
         this._newSummaryItems = [];
         this._longestSummaryItem = null;
+        this._chatSummaryItemCount = 0;

should be named this._chatSummaryItemsCount

@@ +1025,3 @@
         let summaryItem = new SummaryItem(source);
 
+        if(source.isChat) {

Need a space after if.

@@ +1029,3 @@
+            this._chatSummaryItemCount++;
+        } else
+            this._summary.insert_actor(summaryItem.actor, this._chatSummaryItemCount);

Use curly braces here too since we use them in the if clause.

@@ +1127,3 @@
+
+        if (source.isChat)
+            this._chatSummaryItemCount--;

I'd move this right under this._summaryItems.splice(index, 1);

::: js/ui/telepathyClient.js
@@ +490,2 @@
         this._setSummaryIcon(this.createNotificationIcon());
+        this.isChat = true;

It would make sense to move it up to be right under MessageTray.Source.prototype._init.call() since it is a base class field.

Created attachment 179820 [details] [review]
Hope this is final

Created attachment 179823 [details] [review]
Fixes a variable name error w/ ref to the prev patch.