Reduce the runtime of some ACM tests in modules_tests

webrtc/modules/audio_coding/test/TestRedFec.cc

Index: webrtc/modules/audio_coding/test/TestRedFec.cc
diff --git a/webrtc/modules/audio_coding/test/TestRedFec.cc b/webrtc/modules/audio_coding/test/TestRedFec.cc
index d54402657f402a5fadda0cc3c0369ca9f80b90a5..aeb08243c14be552bf425c71f57f01bf84129902 100644
--- a/webrtc/modules/audio_coding/test/TestRedFec.cc
+++ b/webrtc/modules/audio_coding/test/TestRedFec.cc
@@ -12,6 +12,7 @@
 
 #include <assert.h>
 
+#include "webrtc/base/checks.h"
 #include "webrtc/common.h"
 #include "webrtc/common_types.h"
 #include "webrtc/engine_configurations.h"
@@ -453,6 +454,11 @@ int16_t TestRedFec::RegisterSendCodec(char side, const char* codecName,
 void TestRedFec::Run() {
   AudioFrame audioFrame;
   int32_t outFreqHzB = _outFileB.SamplingFrequency();
+  static const int kTestLengthMs = 500;
+  const int test_length_blocks = rtc::CheckedDivExact(kTestLengthMs, 10);
+  _inFileA.SetNum10MsBlocksToRead(test_length_blocks);
+  // Fast-forward 1 second (100 blocks) since the file starts with silence.
+  _inFileA.FastForward(100);
 
   while (!_inFileA.EndOfFile()) {
     EXPECT_GT(_inFileA.Read10MsData(audioFrame), 0);