Add config option to run VideoCodecTest in real time.

It's reasonable to allow clients implementing their own VideoCodecTests
to decide wether they should run in real-time.

Removes the IsAsyncCodec helper, as the assumptions it made are outdated,
and it is no longer useful.

Bug: None
Change-Id: If766935d4947555af54f499a30cfe553bde4c1ab
Reviewed-on: https://webrtc-review.googlesource.com/95722
Commit-Queue: Kári Helgason <kthelgason@webrtc.org>
Reviewed-by: Fredrik Solenberg <solenberg@webrtc.org>
Reviewed-by: Rasmus Brandt <brandtr@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24478}

modules/video_coding/codecs/test/videocodec_test_mediacodec.cc

@@ -35,6 +35,8 @@ VideoCodecTestFixture::Config CreateConfig() {
   config.num_frames = kForemanNumFrames;
   config.hw_encoder = true;
   config.hw_decoder = true;
+  // In order to not overwhelm the OpenMAX buffers in the Android MediaCodec.
+  config.encode_in_real_time = true;
   return config;
 }