Reinstantiate the AudioDecoder tests on Android

The AudioDecoder tests are no longer broken on Android, and can be
re-enabled.

See:

https://logs.chromium.org/logs/chromium/buildbucket/cr-buildbucket.appspot.com/8868055132639161312/+/steps/cast_unittests_on_Android_device_Nexus_5__with_patch_/0/stdout

Bug: 831999
Change-Id: I1d7cbd3adbd1734adc04bd5f0fb6c713815986e3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2433664Reviewed-by: mark a. foltz <mfoltz@chromium.org>
Commit-Queue: Jordan Bayles <jophba@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811343}

media/cast/receiver/audio_decoder_unittest.cc

@@ -238,7 +238,6 @@ TEST_P(AudioDecoderTest, RecoversFromDroppedFrames) {
   WaitForAllAudioToBeDecoded();
 }
 
-#if !defined(OS_ANDROID)  // https://crbug.com/831999
 INSTANTIATE_TEST_SUITE_P(
     AudioDecoderTestScenarios,
     AudioDecoderTest,
@@ -246,7 +245,6 @@ INSTANTIATE_TEST_SUITE_P(
                       TestScenario(CODEC_AUDIO_PCM16, 2, 48000),
                       TestScenario(CODEC_AUDIO_OPUS, 1, 8000),
                       TestScenario(CODEC_AUDIO_OPUS, 2, 48000)));
-#endif
 
 }  // namespace cast
 }  // namespace media