UI: use websocket-based endpoint

Note: This requires rolling a new prebuilt for trace processor
before landing.

Bug: 205274609
Change-Id: I53ab42b9aa6b842012ee155a7e6dcc5ffc562606
diff --git a/CHANGELOG b/CHANGELOG
index 9b62dc9..da2be9b 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -5,7 +5,8 @@
   Trace Processor:
     *
   UI:
-    *
+    * Changed HTTP+RPC to use the /websocket endpoint available in newer
+      versions of trace_processor --httpd.
   SDK:
     *