TraceProcessor: Add ProtoRingBuffer for RPC pipe

ProtoRingBuffer helps tokenizing messages received on
the (upcoming) RPC pipe, so that the underlying stream
(JS<>Wasm postmessage or HTTP) isn't required to deal
with that.

Bug: 159142289
Test: perfetto_unittests --gtest_filter=ProtoRingBufferTest.*
Change-Id: Ic66051c49598f2667b8b32be487b6ea19b3a0353
diff --git a/Android.bp b/Android.bp
index d954988..ae3b5b3 100644
--- a/Android.bp
+++ b/Android.bp
@@ -7606,6 +7606,7 @@
 filegroup {
   name: "perfetto_src_trace_processor_rpc_rpc",
   srcs: [
+    "src/trace_processor/rpc/proto_ring_buffer.cc",
     "src/trace_processor/rpc/query_result_serializer.cc",
     "src/trace_processor/rpc/rpc.cc",
   ],
@@ -7615,6 +7616,7 @@
 filegroup {
   name: "perfetto_src_trace_processor_rpc_unittests",
   srcs: [
+    "src/trace_processor/rpc/proto_ring_buffer_unittest.cc",
     "src/trace_processor/rpc/query_result_serializer_unittest.cc",
   ],
 }