SF: Define mock::MessageQueue

Test: Builds
Bug: 74827900
Change-Id: Id7bed6f01f7df0993c57cb6395b8a0df779ccead
(cherry picked from commit c9903eff3f1dce707e2ea0f26d4e7aa6019d02cd)
diff --git a/services/surfaceflinger/tests/unittests/MockMessageQueue.cpp b/services/surfaceflinger/tests/unittests/MockMessageQueue.cpp
new file mode 100644
index 0000000..62f45ed
--- /dev/null
+++ b/services/surfaceflinger/tests/unittests/MockMessageQueue.cpp
@@ -0,0 +1,27 @@
+/*
+ * Copyright (C) 2018 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "MockMessageQueue.h"
+
+namespace android {
+namespace mock {
+
+// Explicit default instantiation is recommended.
+MessageQueue::MessageQueue() = default;
+MessageQueue::~MessageQueue() = default;
+
+} // namespace mock
+} // namespace android
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