Make sure that ApmHelpersTest tests don't enter a tight loop.

webrtc/media/engine/apm_helpers_unittest.cc

Index: webrtc/media/engine/apm_helpers_unittest.cc
diff --git a/webrtc/media/engine/apm_helpers_unittest.cc b/webrtc/media/engine/apm_helpers_unittest.cc
index 80b03ad0e1c02e965e50491dd0a9155f78d55cbc..8c28db703c01fbb5e6c5d2e64ddea914945f2290 100644
--- a/webrtc/media/engine/apm_helpers_unittest.cc
+++ b/webrtc/media/engine/apm_helpers_unittest.cc
@@ -25,6 +25,11 @@ constexpr AgcConfig kDefaultAgcConfig = { 3, 9, true };
 
 struct TestHelper {
   TestHelper() {
+    // Reply with a 10ms timer every time TimeUntilNextProcess is called to
+    // avoid entering a tight loop on the process thread.
+    EXPECT_CALL(mock_audio_device_, TimeUntilNextProcess())
+        .WillRepeatedly(testing::Return(10));
+
     // This replicates the conditions from voe_auto_test.
     Config config;
     config.Set<ExperimentalAgc>(new ExperimentalAgc(false));