logcat: Create liblogcat

Try to leverage as much of logcat as-is and produce a viable
library API that others can use for their own logcat execution.

Added a test to check ANDROID_PRINTF_LOG environment variable.

Test: gTest logcat-unit-tests
Bug: 35326290
Change-Id: I30de692ea9d83e6fd6e5d9e7cf93d31401a88a40
diff --git a/logcat/logcat_main.cpp b/logcat/logcat_main.cpp
new file mode 100644
index 0000000..9477e79
--- /dev/null
+++ b/logcat/logcat_main.cpp
@@ -0,0 +1,30 @@
+/*
+ * 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.
+ */
+
+#include <signal.h>
+#include <stdlib.h>
+
+#include <log/logcat.h>
+
+int main(int argc, char** argv, char** envp) {
+    android_logcat_context ctx = create_android_logcat();
+    if (!ctx) return -1;
+    signal(SIGPIPE, exit);
+    int retval = android_logcat_run_command(ctx, -1, -1, argc, argv, envp);
+    int ret = android_logcat_destroy(&ctx);
+    if (!ret) ret = retval;
+    return ret;
+}