Introduce proto -> pure c++ code generator

It will be used to generate pure C++ headers / translation units
from trace_config.proto, data_source_config.proto and
data_source_descriptor.proto.
This allows to keep in sync the .proto files and the C++ classes
in tracing/core more easily.
The end goal is to allow clients of the tracing/core API to not
have to depend on libprotobuf (unless their source TraceConfig is
a proto and they want to have that dependency deliberately).

Change-Id: I0fdc53071661bba14af867d01d0a001accc082dc

tools/gen_tracing_cpp_headers_from_protos.py

diff --git a/tools/gen_tracing_cpp_headers_from_protos.py b/tools/gen_tracing_cpp_headers_from_protos.py
new file mode 100755
index 0000000..1ec4a95
--- /dev/null
+++ b/tools/gen_tracing_cpp_headers_from_protos.py
@@ -0,0 +1,55 @@
+#!/usr/bin/env python
+# 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.
+
+import os
+import subprocess
+import sys
+
+PROTOS = (
+  'protos/tracing_service/trace_config.proto',
+  'protos/tracing_service/data_source_config.proto',
+  'protos/tracing_service/data_source_descriptor.proto',
+)
+
+HEADER_PATH = 'include/perfetto/tracing/core'
+CPP_PATH = 'src/tracing/core'
+
+
+def run(cmd):
+  print('\nRunning ' + ' '.join(cmd))
+  subprocess.check_call(cmd)
+
+
+def main():
+  if not os.path.exists('.gn'):
+    print('This script mast be executed from the perfetto root directory')
+    return 1
+  if len(sys.argv) < 2:
+    print('Usage: %s out/xxx' % sys.argv[0])
+    return 1
+  out_dir = sys.argv[1]
+  clang_format = ['clang-format', '-i', '--sort-includes']
+  tool = os.path.join(out_dir, 'proto_to_cpp')
+  if not os.path.exists(tool):
+    print('Could not find %s, run ninja -C %s proto_to_cpp' % (tool, out_dir))
+  for proto in PROTOS:
+    run([tool, proto] + [HEADER_PATH, CPP_PATH])
+    fname = os.path.basename(proto).replace('.proto', '')
+    run(clang_format + [os.path.join(HEADER_PATH, fname + '.h')])
+    run(clang_format + [os.path.join(CPP_PATH, fname + '.cc')])
+
+
+if __name__ == '__main__':
+  sys.exit(main())