Bazel: Add Java target for merged config proto

Change-Id: Ia988c50fea3e49130a20e0b8a80b145b8fa3c569
diff --git a/BUILD.extras b/BUILD.extras
index 732f3f8..a72041f 100644
--- a/BUILD.extras
+++ b/BUILD.extras
@@ -43,6 +43,13 @@
     ],
 )
 
+perfetto_java_proto_library(
+    name = "protos_perfetto_trace_merged_config_java",
+    deps = [
+        ":protos_perfetto_trace_merged_config_protos",
+    ],
+)
+
 perfetto_gensignature_internal_only(
     name = "trace_processor_sig",
     srcs = [