Reduce the runtime of some ACM tests in modules_tests

webrtc/modules/audio_coding/test/iSACTest.cc

Index: webrtc/modules/audio_coding/test/iSACTest.cc
diff --git a/webrtc/modules/audio_coding/test/iSACTest.cc b/webrtc/modules/audio_coding/test/iSACTest.cc
index 09744b13c61436970eea97a693e3fde15cfff214..ec4233b8451a2da61eca53ca19dbc657aebdf5cc 100644
--- a/webrtc/modules/audio_coding/test/iSACTest.cc
+++ b/webrtc/modules/audio_coding/test/iSACTest.cc
@@ -23,6 +23,7 @@
 #include <time.h>
 #endif
 
+#include "webrtc/base/checks.h"
 #include "webrtc/modules/audio_coding/acm2/acm_common_defs.h"
 #include "webrtc/modules/audio_coding/test/utility.h"
 #include "webrtc/system_wrappers/include/event_wrapper.h"
@@ -117,6 +118,11 @@ void ISACTest::Setup() {
   EXPECT_EQ(0, _acmA->RegisterSendCodec(_paramISAC32kHz));
 
   _inFileA.Open(file_name_swb_, 32000, "rb");
+  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 files start with silence.
+  _inFileA.FastForward(100);
   std::string fileNameA = webrtc::test::OutputPath() + "testisac_a.pcm";
   std::string fileNameB = webrtc::test::OutputPath() + "testisac_b.pcm";
   _outFileA.Open(fileNameA, 32000, "wb");