Reduce the runtime of some ACM tests in modules_tests

webrtc/modules/audio_coding/test/EncodeDecodeTest.cc

Index: webrtc/modules/audio_coding/test/EncodeDecodeTest.cc
diff --git a/webrtc/modules/audio_coding/test/EncodeDecodeTest.cc b/webrtc/modules/audio_coding/test/EncodeDecodeTest.cc
index ef45705e20aac0b1b984911d249b6415a3c28f7f..e0222afbe07b76d8db0e93928e43fd7ef1834b61 100644
--- a/webrtc/modules/audio_coding/test/EncodeDecodeTest.cc
+++ b/webrtc/modules/audio_coding/test/EncodeDecodeTest.cc
@@ -63,6 +63,10 @@ void Sender::Setup(AudioCodingModule *acm, RTPStream *rtpStream,
   if (channels == 2) {
     _pcmFile.ReadStereo(true);
   }
+  // Set test length to 500 ms (50 blocks of 10 ms each).
+  _pcmFile.SetNum10MsBlocksToRead(50);
+  // Fast-forward 1 second (100 blocks) since the file starts with silence.
+  _pcmFile.FastForward(100);
 
   // Set the codec for the current test.
   if ((testMode == 0) || (testMode == 1)) {