profiling: Add proto for heapprofd.

This is unused for now but will be used for integrating heapprofd with Perfetto.

Change-Id: Ib4619fdf7983e5e4fb4207de8df60b60ed729385
diff --git a/BUILD.gn b/BUILD.gn
index 645b3a5..7cfc772 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -54,6 +54,8 @@
       ":traced",
       ":traced_probes",
       "protos/perfetto/config:merged_config",  # For syntax-checking the proto.
+      "protos/perfetto/profiling:lite",  # For syntax-checking the proto.
+                                         # TODO(fmayer): Remove once used.
       "src/ipc/protoc_plugin:ipc_plugin($host_toolchain)",
       "tools:protoc_helper",
     ]