Support partners to expose their own system libs to Android apps

Partners (entities other than AOSP) can expose their own system
libraries which are in /system/lib[64] to Android apps. This can be done
by adding the name of the libs into the files
/system/etc/public.libraries-<companyname>.txt.

There can be multiple of the txt files on a device, which is for the
case that multiple partners contributing to the same system image
have their own set of public libraries.

The public libraries MUST be named as lib<name>.<companyname>.so. This
is to prevent accidental exposure of AOSP-defined system private libs.

Note 1:
<companyname> doesn't need to be the same as the value of the sysprop
ro.product.manufacturer or anything that can be part of a file path.

Note 2:
This feature is not for exposing SoC-specific libs to Android apps. That
is already done by /vendor/etc/public.libraries.txt and is only for
libs in /vendor/lib[64].

Bug: 68280171
Test: mm -j under /system/core/libnativeloader/test
cts-tradefed run commandAndExit cts-dev -m CtsJniTestCases -t
android.jni.cts.JniStaticTest#test_linker_namespaces

Change-Id: I7d32ec27c7858e35b96c7c98223cc110acb35b81
diff --git a/libnativeloader/test/test.cpp b/libnativeloader/test/test.cpp
new file mode 100644
index 0000000..b166928
--- /dev/null
+++ b/libnativeloader/test/test.cpp
@@ -0,0 +1,21 @@
+/*
+ * Copyright (C) 2017 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.
+ */
+#define LOG_TAG "oemlib"
+#include <android-base/logging.h>
+
+static __attribute__((constructor)) void test_lib_init() {
+  LOG(DEBUG) << LIBNAME << " loaded";
+}