Extract functionality of test_main into separate library.

Extract functionality of test_main into separate library to be able to
reuse it if another main will be required.

Bug: webrtc:5996
Change-Id: I2925b4240bd0e4fb884b43bb16667ca2d6216bbd
Reviewed-on: https://webrtc-review.googlesource.com/c/105921
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Artem Titov <titovartem@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25172}

test/test_main_lib.h

@@ -0,0 +1,38 @@
+/*
+ *  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.
+ */
+#ifndef TEST_TEST_MAIN_LIB_H_
+#define TEST_TEST_MAIN_LIB_H_
+
+#include <memory>
+
+namespace webrtc {
+
+// Class to initialize test environment and run tests.
+class TestMain {
+ public:
+  virtual ~TestMain() {}
+
+  static std::unique_ptr<TestMain> Create();
+
+  // Initializes test environment. Clients can add their own initialization
+  // steps after call to this method and before running tests.
+  // Returns 0 if initialization was successful and non 0 otherwise.
+  virtual int Init(int argc, char* argv[]) = 0;
+
+  // Runs test end return result error code. 0 - no errors.
+  virtual int Run(int argc, char* argv[]) = 0;
+
+ protected:
+  TestMain() = default;
+};
+
+}  // namespace webrtc
+
+#endif  // TEST_TEST_MAIN_LIB_H_