Update release notes for 2.9.0

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=214784773

RELEASENOTES.md

 # Release notes #
 
-### dev-v2 (not yet released) ###
-
-* Allow setting log level for ExoPlayer logcat output
-  ([#4665](https://github.com/google/ExoPlayer/issues/4665)).
-* Fix an issue where audio and video would desynchronize when playing
-  concatenations of gapless content
-  ([#4559](https://github.com/google/ExoPlayer/issues/4559)).
-
 ### 2.9.0 ###
 
 * Turn on Java 8 compiler support for the ExoPlayer library. Apps that depend
@@ -26,6 +18,8 @@
 * Allow passing a `Looper`, which specifies the thread that must be used to
   access the player, when instantiating player instances using
   `ExoPlayerFactory` ([#4278](https://github.com/google/ExoPlayer/issues/4278)).
+* Allow setting log level for ExoPlayer logcat output
+  ([#4665](https://github.com/google/ExoPlayer/issues/4665)).
 * Simplify `BandwidthMeter` injection: The `BandwidthMeter` should now be
   passed directly to `ExoPlayerFactory`, instead of to `TrackSelection.Factory`
   and `DataSource.Factory`. The `BandwidthMeter` is passed to the components
@@ -148,6 +142,9 @@
 * Fix bug preventing use of multiple key session support (`multiSession=true`)
   for non-Widevine `DefaultDrmSessionManager` instances
   ([#4834](https://github.com/google/ExoPlayer/issues/4834)).
+* Fix issue where audio and video would desynchronize when playing
+  concatenations of gapless content
+  ([#4559](https://github.com/google/ExoPlayer/issues/4559)).
 * IMA extension:
   * Refine the previous fix for empty ad groups to avoid discarding ad breaks
     unnecessarily ([#4030](https://github.com/google/ExoPlayer/issues/4030) and