Add the ability to dump initial recipe properties.

recipe_engine/arguments.proto

Index: recipe_engine/arguments.proto
diff --git a/recipe_engine/arguments.proto b/recipe_engine/arguments.proto
index 750f1fb385f442f00612ba731f7551544ef0c3d1..e639466d9979435e435d00e5c715339c5f36bc44 100644
--- a/recipe_engine/arguments.proto
+++ b/recipe_engine/arguments.proto
@@ -57,6 +57,10 @@ message Arguments {
   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;