[corelib] dart:developer timeline flow events

CHANGELOG.md

 ## 1.25.0
 
 ### Language
 * A string in a `part of` declaration may now be used to refer to the library
   this file is part of.
   A library part can now declare its library either as:
   `part of name.of.library;` or as `part of "uriReferenceOfLibrary.dart";`.
   This allows libraries with no library declarations (and therefore no name)
   to have parts, and it allows tools to easily find the library of a part
   file.
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     'SecureSocket.connect' and 'RawSecureSocket.connect. If a connection attempt
     takes longer than the duration specified in 'timeout', a 'SocketException'
     will be thrown. Note: if the duration specified in 'timeout' is greater than
     the system level timeout duration, a timeout may occur sooner than specified
     in 'timeout'.
 
 * `dart:core`
   * The `Uri` class now correctly handles paths while running on Node.js on
     Windows.
 
+* `dart:developer`
+  * `Timeline.startSync` and `Timeline.timeSync` now accept an optional
+    parameter `flow` of type `Flow`. The `flow` parameter is used to generate
+    flow timeline events that are enclosed by the slice described by
+    `Timeline.{start,finish}Sync` and `Timeline.timeSync`.
+
 ### Dart VM
 * Support for MIPS has been remvoed.
 
 ### Tool Changes
 
 * Pub
 
   * Git dependencies may now include a `path` parameter, indicating that the
     package exists in a subdirectory of the Git repository. For example:
 
@@ skipping 2117 matching lines @@
     they will keep the Dart process alive until they time out. This fixes the
     handling of persistent connections. Previously, the client would shut down
     immediately after a request.
 
   * **Breaking change:** `HttpServer` no longer compresses all traffic by
     default. The new `autoCompress` property can be set to `true` to re-enable
     compression.
 
 * `dart:isolate`: `Isolate.spawnUri` added the optional `packageRoot` argument,
   which controls how it resolves `package:` URIs.