Remove AudioDeviceObserver and make ADM not inherit from the Module interface.

media/engine/apm_helpers_unittest.cc

Index: media/engine/apm_helpers_unittest.cc
diff --git a/media/engine/apm_helpers_unittest.cc b/media/engine/apm_helpers_unittest.cc
index 315cdc855306ab34c6e652c55e9d727cffbb87aa..ff9308a47e330acf51025b801737ce6e341e0ac4 100644
--- a/media/engine/apm_helpers_unittest.cc
+++ b/media/engine/apm_helpers_unittest.cc
@@ -25,11 +25,6 @@ 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));