Add LogDog / annotation protobuf support.

recipe_engine/arguments.proto

 // Copyright 2016 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 syntax = "proto3";
 
 package recipe_engine;
 
 // Arguments is a protobuf that can be supplied to the recipe engine through its
 // "--operational-args-path" command-line parameter in JSONPB format.
@@ skipping 46 matching lines @@
   message AnnotationFlags {
     // If true, emit CURRENT_TIMESTAMP annotations.
     bool emit_timestamp = 1;
 
     // If true, emit all input properties as annotations at the beginning of
     // recipe engine execution.
     bool emit_initial_properties = 2;
   }
   // Annotation control flags.
   AnnotationFlags annotation_flags = 2;
+
+  // LogDog flags.
+  //
+  // If the "streamserver_uri" is provided, recipe output will be forwarded
+  // through LogDog streams using Milo's Annotation Protobuf instead of
+  // STDOUT/STDERR and classic @@@annotations@@@.
+  message LogDogFlags {
+    // The LogDog streamserver URI.
+    string streamserver_uri = 1;
+
+    // The log stream base name. If provided, generated stream names will be
+    // prefixed with "<name_base>/". This must be a valid LogDog stream name.
+    string name_base = 2;
+
+    // If true, tee output through STDOUT/STDERR using inline @@@annotation@@@
+    // markers in addition to LogDog streaming.
+    bool tee = 3;
+  }
+  LogDogFlags logdog = 3;
 }