libdebuggerd: add protobuf implementation.

This commit implements protobuf output for tombstones, along with a
translator that should emit bytewise identical output to the existing
tombstone dumping code, except for ancillary data from GWP-ASan and
Scudo, which haven't been implemented yet.

Test: setprop debug.debuggerd.translate.translate_proto_to_text 1 &&
        /data/nativetest64/debuggerd_test/debuggerd_test
Test: for TOMBSTONE in /data/tombstones/tombstone_??; do
        pbtombstone $TOMBSTONE.pb | diff $TOMBSTONE -
      done
Change-Id: Ieeece6e6d1c26eb608b00ec24e2e725e161c8c92
diff --git a/debuggerd/pbtombstone.cpp b/debuggerd/pbtombstone.cpp
new file mode 100644
index 0000000..7527e31
--- /dev/null
+++ b/debuggerd/pbtombstone.cpp
@@ -0,0 +1,62 @@
+/*
+ * 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.
+ */
+
+#include <err.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <unistd.h>
+
+#include <android-base/unique_fd.h>
+#include <libdebuggerd/tombstone.h>
+
+#include "tombstone.pb.h"
+
+using android::base::unique_fd;
+
+[[noreturn]] void usage(bool error) {
+  fprintf(stderr, "usage: pbtombstone TOMBSTONE.PB\n");
+  fprintf(stderr, "Convert a protobuf tombstone to text.\n");
+  exit(error);
+}
+
+int main(int argc, const char* argv[]) {
+  if (argc != 2) {
+    usage(true);
+  }
+
+  if (strcmp("-h", argv[1]) == 0 || strcmp("--help", argv[1]) == 0) {
+    usage(false);
+  }
+
+  unique_fd fd(open(argv[1], O_RDONLY | O_CLOEXEC));
+  if (fd == -1) {
+    err(1, "failed to open tombstone '%s'", argv[1]);
+  }
+
+  Tombstone tombstone;
+  if (!tombstone.ParseFromFileDescriptor(fd.get())) {
+    err(1, "failed to parse tombstone");
+  }
+
+  bool result = tombstone_proto_to_text(
+      tombstone, [](const std::string& line, bool) { printf("%s\n", line.c_str()); });
+
+  if (!result) {
+    errx(1, "tombstone was malformed");
+  }
+
+  return 0;
+}