Allow for embedder provided service request handlers

runtime/vm/json_stream.h

Index: runtime/vm/json_stream.h
diff --git a/runtime/vm/json_stream.h b/runtime/vm/json_stream.h
index 548e5538ad05c42187a14399dc9732dcea2bc27e..ba09e5d079a0736d6dbe0c7bd6cb4e10bb54913d 100644
--- a/runtime/vm/json_stream.h
+++ b/runtime/vm/json_stream.h
@@ -56,6 +56,11 @@ class JSONStream : ValueObject {
 
   const char* LookupOption(const char* key) const;
 
+  const char* command() const { return command_; }
+  const char** arguments() const { return arguments_; }
+  const char** option_keys() const { return option_keys_; }
+  const char** option_values() const { return option_values_; }
+
  private:
   void Clear();