libbinder_ndk: test Bp destruction

When sending a binder to another process, there are two things that
delay the destruction:
- there is a separate queue, flushed with 'flushCommands' that must be
emptied in the remote process
- the client thread must process the refcount loss asynchronously

This CL works around both of these problems by explicitly flushing
commands and waiting for the thread to process the refcount.

Bug: 148287051
Test: libbinder_ndk_unit_test
Change-Id: I2687b429faae659d80406f0b418c96a1eb40e9bd
diff --git a/libs/binder/ndk/test/IBinderNdkUnitTest.aidl b/libs/binder/ndk/test/IBinderNdkUnitTest.aidl
new file mode 100644
index 0000000..6e8e463
--- /dev/null
+++ b/libs/binder/ndk/test/IBinderNdkUnitTest.aidl
@@ -0,0 +1,27 @@
+/*
+ * Copyright (C) 2020 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.
+ */
+
+// This AIDL is to test things that can't be tested in CtsNdkBinderTestCases
+// because it requires libbinder_ndk implementation details or APIs not
+// available to apps. Please prefer adding tests to CtsNdkBinderTestCases
+// over here.
+
+import IEmpty;
+
+interface IBinderNdkUnitTest {
+    void takeInterface(IEmpty test);
+    void forceFlushCommands();
+}