PERF: Don't display days ago on timeline for megatopics.

Analysis using `pg_stat_statements` showed this query
to be eating up a significant portion of CPU.

spec/components/topic_view_spec.rb

@@ -549,4 +549,30 @@ describe TopicView do
       end
     end
   end
+
+  describe '#filtered_post_stream' do
+    let!(:post) { Fabricate(:post, topic: topic, user: first_poster) }
+    let!(:post2) { Fabricate(:post, topic: topic, user: evil_trout) }
+    let!(:post3) { Fabricate(:post, topic: topic, user: first_poster) }
+
+    it 'should return the right columns' do
+      expect(topic_view.filtered_post_stream).to eq([
+        [post.id, post.post_number, 0],
+        [post2.id, post2.post_number, 0],
+        [post3.id, post3.post_number, 0]
+      ])
+    end
+
+    describe 'for mega topics' do
+      it 'should return the right columns' do
+        SiteSetting.auto_close_topics_post_count = 2
+
+        expect(topic_view.filtered_post_stream).to eq([
+          [post.id, post.post_number],
+          [post2.id, post2.post_number],
+          [post3.id, post3.post_number]
+        ])
+      end
+    end
+  end
 end