Reduce the runtime of some ACM tests in modules_tests

webrtc/modules/audio_coding/test/TestStereo.cc

Index: webrtc/modules/audio_coding/test/TestStereo.cc
diff --git a/webrtc/modules/audio_coding/test/TestStereo.cc b/webrtc/modules/audio_coding/test/TestStereo.cc
index 19f027b0582ec7dd86e08f0228cadd8827d75d4c..5fc4f5cde8975baa26a6bb678b8ff7d995e2e1b9 100644
--- a/webrtc/modules/audio_coding/test/TestStereo.cc
+++ b/webrtc/modules/audio_coding/test/TestStereo.cc
@@ -15,6 +15,7 @@
 #include <string>
 
 #include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/base/checks.h"
 #include "webrtc/common_types.h"
 #include "webrtc/engine_configurations.h"
 #include "webrtc/modules/audio_coding/include/audio_coding_module_typedefs.h"
@@ -735,6 +736,13 @@ void TestStereo::Run(TestPackStereo* channel, int in_channels, int out_channels,
   int error_count = 0;
   int variable_bytes = 0;
   int variable_packets = 0;
+  static const int kTestLengthMs = 500;
+  const int test_length_blocks = rtc::CheckedDivExact(kTestLengthMs, 10);
+  in_file_mono_->SetNum10MsBlocksToRead(test_length_blocks);
+  in_file_stereo_->SetNum10MsBlocksToRead(test_length_blocks);
+  // Fast-forward 1 second (100 blocks) since the files start with silence.
+  in_file_stereo_->FastForward(100);
+  in_file_mono_->FastForward(100);
 
   while (1) {
     // Simulate packet loss by setting |packet_loss_| to "true" in
@@ -800,7 +808,7 @@ void TestStereo::Run(TestPackStereo* channel, int in_channels, int out_channels,
   // such as Opus.
   if (variable_packets > 0) {
     variable_bytes /= variable_packets;
-    EXPECT_NEAR(variable_bytes, pack_size_bytes_, 3);
+    EXPECT_NEAR(variable_bytes, pack_size_bytes_, 18);
   }
 
   if (in_file_mono_->EndOfFile()) {