Reland Update CHANGELOG for v19

This is a reland of aosp/1817353 + aosp/1817346.

Change-Id: I1eb2da95929a23ff4d98da42897f54bdc8ea102e
diff --git a/CHANGELOG b/CHANGELOG
index a117359..7fc812f 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -9,6 +9,31 @@
     *
 
 
+v19.0 - 2021-09-02:
+  Tracing service and probes:
+    * Added ftrace clock reporting to the trace.
+  Trace Processor:
+    * Added support for longs/doubles to RUN_METRIC.
+    * Added power profile data for sunfish, redfin, and bramble.
+    * Added experimental Python library for computing slice breakdowns.
+    * Fixed parsing of JSON escape sequences.
+    * Fixed JSON trace detection.
+  UI:
+    * Added local cacheing of traces. Traces are reloaded in case of refresh or
+      tab being discarded by the browser.
+    * Added icon to distinguish metric-derived tracks.
+    * Added release channel selector to feature flags page.
+    * Fixed crash with null slice names.
+  SDK:
+    * Added some missing NESTABLE_ASYNC legacy trace macros.
+    * Fixed reporting of producer uid in --query.
+    * Fixed version numbering scheme for minor versions. Previously versions
+      were numbered as like v19.0.42 where 42 represented the number of commits
+      since the last major version release. This was ambiguous in the presence
+      of branches. Now versions are numbered like v19.0-ab12cd34 where ab12cd34
+      is the shortened Git commit-ish.
+
+
 v18.0 - 2021-08-02:
   Tracing service and probes:
     * Added cross-compiler toolchains for Linux-{arm,64} based on Debian Sid.