Generate ftrace event descriptors

In order to parse unknown ftrace events we need to know the names
and fields of each event.

Bug:120012594
Change-Id: I797a436507c6f535e05a7656f07bdc28f9a5a109
diff --git a/Android.bp b/Android.bp
index 5a6a79b..ef9cd99 100644
--- a/Android.bp
+++ b/Android.bp
@@ -2559,6 +2559,7 @@
     "src/tracing/test/mock_producer.cc",
     "src/tracing/test/test_shared_memory.cc",
     "src/tracing/test/tracing_integration_test.cc",
+    "tools/ftrace_proto_gen/ftrace_descriptor_gen.cc",
     "tools/ftrace_proto_gen/ftrace_proto_gen.cc",
     "tools/ftrace_proto_gen/ftrace_proto_gen_unittest.cc",
     "tools/ftrace_proto_gen/proto_gen_utils.cc",