Suppress ProGuard warnings about javax.annotation

These annotations are compile-only - so we don't mind they're not
accessible at runtime.

PiperOrigin-RevId: 285993063

RELEASENOTES.md

@@ -32,6 +32,8 @@
   ([#6753](https://github.com/google/ExoPlayer/issues/6753)).
 * AV1 extension: Fix ProGuard rules
   ([6773](https://github.com/google/ExoPlayer/issues/6773)).
+* Suppress ProGuard warnings for compile-time `javax.annotation` package
+  ([#6771](https://github.com/google/ExoPlayer/issues/6771)).
 
 ### 2.11.0 (2019-12-11) ###
 

library/core/proguard-rules.txt

@@ -65,6 +65,7 @@
 # Don't warn about checkerframework and Kotlin annotations
 -dontwarn org.checkerframework.**
 -dontwarn kotlin.annotations.jvm.**
+-dontwarn javax.annotation.**
 
 # Some members of this class are being accessed from native methods. Keep them unobfuscated.
 -keep class com.google.android.exoplayer2.ext.video.VideoDecoderOutputBuffer {