Move libstatssocket from frameworks/base to system/core/

So that lmkd can build on PDK.

Bug: 79349329
Test: builds locally
Change-Id: I981e6ef9f9769b873640e5f169a9495ccea2f25c
diff --git a/libstats/statsd_writer.h b/libstats/statsd_writer.h
new file mode 100644
index 0000000..82e14e0
--- /dev/null
+++ b/libstats/statsd_writer.h
@@ -0,0 +1,43 @@
+/*
+ * 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.
+ */
+
+#ifndef ANDROID_STATS_LOG_STATS_WRITER_H
+#define ANDROID_STATS_LOG_STATS_WRITER_H
+
+#include <pthread.h>
+#include <stdatomic.h>
+#include <sys/socket.h>
+
+/**
+ * Internal lock should not be exposed. This is bad design.
+ * TODO: rewrite it in c++ code and encapsulate the functionality in a
+ * StatsdWriter class.
+ */
+void statsd_writer_init_lock();
+int statsd_writer_init_trylock();
+void statsd_writer_init_unlock();
+
+struct android_log_transport_write {
+    const char* name; /* human name to describe the transport */
+    atomic_int sock;
+    int (*available)(); /* Does not cause resources to be taken */
+    int (*open)();      /* can be called multiple times, reusing current resources */
+    void (*close)();    /* free up resources */
+    /* write log to transport, returns number of bytes propagated, or -errno */
+    int (*write)(struct timespec* ts, struct iovec* vec, size_t nr);
+};
+
+#endif  // ANDROID_STATS_LOG_STATS_WRITER_H