Add unit tests for Android audio device module

The tests are a combination of the old audio_device_unittest.cc and
audio_manager_unittest.cc, with the exception of a few that were no
longer relevant.

RunPlayoutAndRecordingInFullDuplex remains disabled according to its
comment, but has been verified to pass on at least one device.
MeasureLoopbackLatency also remains disabled, but has not been tested due
to lack of necessary hardware.

Bug: webrtc:7452
Change-Id: Ie361bc8f5e1990729d7b4699faf2a73abe3cbe8d
Reviewed-on: https://webrtc-review.googlesource.com/69340
Reviewed-by: Henrik Andreassson <henrika@webrtc.org>
Reviewed-by: Magnus Jedvert <magjed@webrtc.org>
Commit-Queue: Paulina Hensman <phensman@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22836}

sdk/android/native_unittests/org/webrtc/ApplicationContextProvider.java

@@ -0,0 +1,20 @@
+/*
+ *  Copyright (c) 2018 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+package org.webrtc;
+
+import android.content.Context;
+
+public class ApplicationContextProvider {
+  @CalledByNative
+  public static Context getApplicationContextForTest() {
+    return ContextUtils.getApplicationContext();
+  }
+}