tracing: Add ActivateTriggers function.

Instead of shelling out and executing `trigger_perfetto <trigger>`, a
process using the perfetto SDK can call
`perfetto::Tracing::ActivateTriggers({"<trigger>"})`.

Bug: 258465428

Change-Id: Ic8f0458684d87099d05ff18ba87831158bc5be4a
diff --git a/CHANGELOG b/CHANGELOG
index a0d4c7b..857b4aa 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -6,7 +6,7 @@
   UI:
     *
   SDK:
-    *
+    * Add perfetto::Tracing::ActivateTriggers() function.
 
 
 v31.0 - 2022-11-10: