Add the ability to dump initial recipe properties.

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 39 matching lines @@
     map<string, Property> property = 1;
   }
 
   // Input Properties.
   PropertyMap properties = 1;
 
   // Message containing the set of supported annotation control flags.
   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;
 }