Tracing V2 prototype [NOT FOR REVIEW]

base/trace_event/common/proto/events_chunk.proto

+syntax = "proto2";
+option optimize_for = LITE_RUNTIME;
+
+package tracing;
+
+message EventsChunk {
+  // Chunks produced by the same trace writer have the same stream_id.
+  // This is to look up the next chunk for a given thread.
+  required uint32 stream_id = 1;
+
+  // A monotonic counter within stream_id. To order chunks within the stream.
+  required uint32 seq_id_in_stream = 2;
+
+  // Each event is a byte sequence that encapsulates the bytes for a single
+  // Event (see event.proto) or an incomplete portion of it.
+  // Why this isn't just a "repeated Events" field? An Event can spawn across
+  // several chunks. In this case the reader has to first glue the byte
+  // sequences together and then process the event.
+  repeated bytes events = 3;
+  optional bool first_event_continues_from_prev_chunk = 4;
+  optional bool last_event_continues_on_next_chunk = 5;
+
+  required uint32 num_events = 6;  // TODO here for streaming: fixed?
+}