Update CHANGELOG/@Since of feature that didn't make 2.15.

Change-Id: Iee1ee36e3de040da2d2508938ba00a7faa1950c6
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/219980
Reviewed-by: Alexander Thomas <athom@google.com>
Commit-Queue: Lasse R.H. Nielsen <lrn@google.com>

CHANGELOG.md

@@ -1,5 +1,13 @@
 ## 2.16.0
 
+### Core libraries
+
+#### `dart:core`
+
+- Add `Error.throwWithStackTrace` which can `throw` an
+  error with an existing stack trace, instead of creating
+  a new stack trace.
+
 ### Tools
 
 #### Dart command line
@@ -323,9 +331,6 @@ them, you must set the lower bound on the SDK constraint for your package to
   ready to be removed.
   Code catching the class should move to catching `Error` instead
   (or, for integers, check first for whether it's dividing by zero).
-- Add `Error.throwWithStackTrace` which can `throw` an
-  error with an existing stack trace, instead of creating
-  a new stack trace.
 
 #### `dart:io`
 

sdk/lib/core/errors.dart

@@ -101,7 +101,7 @@ class Error {
   /// or set on [error] if it is an [Error],
   /// may not be the [stackTrace] object itself,
   /// but will be a stack trace with the same content.
-  @Since("2.15")
+  @Since("2.16")
   static Never throwWithStackTrace(Object error, StackTrace stackTrace) {
     checkNotNullable(error, "error");
     checkNotNullable(stackTrace, "stackTrace");