Fix lock behavior on RTCAudioSession.

webrtc/modules/audio_device/ios/objc/RTCAudioSessionTest.mm

+/*
+ *  Copyright 2016 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.
+ */
+
+#import <Foundation/Foundation.h>
+
+#include "testing/gtest/include/gtest/gtest.h"
+
+#import "webrtc/modules/audio_device/ios/objc/RTCAudioSession.h"
+
+@interface RTCAudioSessionTest : NSObject
+
+- (void)testLockForConfiguration;
+
+@end
+
+@implementation RTCAudioSessionTest
+
+- (void)testLockForConfiguration {
+  RTCAudioSession *session = [RTCAudioSession sharedInstance];
+
+  for (size_t i = 0; i < 2; i++) {
+    [session lockForConfiguration];
+    EXPECT_TRUE(session.isLocked);
+  }
+  for (size_t i = 0; i < 2; i++) {
+    EXPECT_TRUE(session.isLocked);
+    [session unlockForConfiguration];
+  }
+  EXPECT_FALSE(session.isLocked);
+}
+
+@end
+
+TEST(RTCAudioSessionTest, LockForConfiguration) {
+  RTCAudioSessionTest *test = [[RTCAudioSessionTest alloc] init];
+  [test testLockForConfiguration];
+}